I heard that at the Beginning The Creator of DBZ was gonna make Frieza a Girl but he Changed it because he didn't want Goku to Hit a Girl!
Well thats why "he" has a girly voice ^^ but I believe that he didnt change her gender... lol

Now wikipedia about Frieza:

Frieza had many races under his thumb in his planetary trade, but none were as prevalent as the Saiyans. Gifted with natural fighting ability, strength and the ability to become stronger after every battle, Saiyans became powerful weapons in Frieza's subjugation of planets. However, these very abilities made them a liability to the paranoid Frieza, afraid that, left unchecked, the Saiyans could either unite and overwhelm him, or one day provide a warrior to rival Frieza himself. With the advice of his top henchman Zarbon, Frieza plans to wipe out the Saiyan race.

Hearing the accomplishments of the low-level Saiyan Bardock and acting on his own fears of the Super Saiyan legend, Frieza resolves to eliminate all possible threats. He sends his henchman Dodoria and his elites to assassinate Bardock and his team, while Frieza himself sets a course to the Saiyan homeworld. On his arrival, King Vegeta and his men attempt an uprising after Vegeta is kidnapped, ending with the King and his soldiers being slaughtered by Frieza as Zarbon and Dodoria watch.

As Frieza arrived in the planet's orbit he was confronted by a charging Bardock, lunging through the fields of Frieza's men, and in defiance of the tyrant, even goes as far as to fire a ki blast at Frieza, to which the tyrant retaliated by laughing maniacally with insane glee as he prepared a Supernova attack to annihilate the planet. The attack consumes Bardock, and even some of his men as it buries itself deep beneath the planet's surface resulting in a massive explosion, eradicating nearly every Saiyan.

After the planet's explosion, a story was fabricated to ensure the loyalty of the few remaining Saiyans Frieza had kept in his employ as a convenience, Vegeta, Raditz and Nappa. According to the myth that was created, the guardian of Planet Vegeta, ashamed at the immorality of the Saiyans, summoned meteors to impact and destroy the planet and the Saiyan race. It is shown in a flashback during the Frieza Saga that Frieza's destruction of the Saiyans was a rumor that Vegeta heard before the events of Dragon Ball Z, although this is a form of retroactive continuity, as Vegeta is shown to be unaware of this until Dodoria's confession before his death.
[edit] Planet Namek
Frieza with his top two henchmen, Zarbon and Dodoria.

Twenty-four years later, Frieza spies on Vegeta's scouter during the Saiyan Saga and in doing so, learns of the existence of the Dragon Balls on Planet Namek. Planning to obtain them and make a wish for immortality, Frieza arrives on Namek with his longtime comrades and top two highest ranking henchmen, Zarbon and Dodoria, in order to try and obtain the Dragon Balls from the Namekians. After Cui, Dodoria, and Zarbon fall to Vegeta, who had betrayed Frieza to collect the fabled items for his own ends, the Ginyu Force is summoned by Frieza to retrieve the Dragon Balls and neutralize the Saiyan rogue so that he can be brought to him, but fail to do so when Goku arrives at Planet Namek and fights them, eventually defeating them.

While searching for the remaining Dragon Balls, Frieza arrives at Guru's home and is confronted by Nail, the strongest of the Namekian warriors. Frieza horribly tortures Nail and in an attempt to reveal the password of the Dragon Balls (and in the process causes Guru's death under the strain of Frieza's torture), then leaving him to die after discovering the fight was a diversion for Dende to reveal the password to Krillin and Gohan as they take the Dragon Balls. Frieza, enraged, follows in pursuit of the heroes only to find that Porunga, the Namekian Dragon is gone due to Guru's death. He is faced with a much more powerful Vegeta, who is now capable of possibly holding his own for a bit against Frieza's strength.
Frieza's first form, without the Saiyan battle fatigue adorned for the majority of his appearances in this state.

Spurred on by Vegeta, Frieza unveils his second form, allowing him to defeat Vegeta and critically injure Krillin, taunting Gohan with his friend's limp body. Gohan responds in an incredible fury and proceeds to pound Frieza with punches, kicks and a barrage of ki blasts. Frieza then proceeds to pummel him in return, but Krillin, healed by Dende shoots a Destructo Disk at his tail, chopping a portion of it off. Frieza chases Krillin in a diversion and returns to the others when Frieza decides to finish them off. Fortunately, Piccolo joins the battle - only slightly lesser in abilities to Frieza, thanks to a merging with the dying Nail.
Frieza impales Krillin on his horn.

Eager to demonstrate even more of his power to Piccolo, Frieza again transformed, unlocking more of his power and enabling him to brutally lay waste to his opponent. Gohan again gets angry and fires a huge bolt of ki, which Frieza deflects back. Piccolo protects Gohan by firing a blast at it, deflecting it away. Frieza notes Gohan's growing power, and notices he is a Saiyan, but doubts Vegeta is his father (he still believes that only Raditz, Nappa, and Vegeta escaped Planet Vegeta's destruction) and finally he unveils his true form, stressing that he intended to give his foes the "pleasure" of observing it before they died — in the anime, he promises to show them "a terror greater than hell." In his new form, Frieza first killed Dende, who had been healing the heroes. Vegeta announced himself as a Super Saiyan, and fought Frieza but the tyrant was still far his superior, and proceeded to punish him after Vegeta lost his hope. Just as Frieza was about to slay Vegeta, the healed Goku arrives on the battlefield, ready to fight Frieza. Vegeta, believing that Goku had finally become a full-fledged Super Saiyan, taunts Frieza, even though he is too badly beaten to even stand. Frieza, proud of his past accomplishments, smirks before sending his Death Beam through the Saiyan Prince's heart. Teetering on the brink of death, Vegeta is able to tell the newly-healed Goku of Frieza's genocide of the Saiyan race, imploring him to take revenge on behalf for all Saiyans. As Vegeta finishes his plea to Goku, he dies. Goku, saddened by Vegeta's death, buries him and vows to finish Frieza. Goku and Frieza then spar, with Frieza realizing that his opponent is the son of the Saiyan that gave him such trouble years before. Goku and Frieza are an even match for a while (with the latter even admitting that Goku is the first person other than his parents to cause him pain in his true form), until Frieza determines and states that with 50%, he could defeat Goku. Frieza then increases his power to 50% of his maximum, and easily beats Goku, with Goku completely unable to keep up. Goku attempts to use his Kaioken x10 during this battle, but Frieza stills beats him using half of his maximum power. Goku attempts to use a Kaioken x20 and a Kamehameha attack, but to no significant avail (the best he could do was slightly char Frieza's hands), as Frieza easily diffuses the blast with 50% of his power. However, he does become alarmingly aware of his opponent's remarkable abilities.
Frieza is sliced by his own attack.

It should be noted that in the English dub, Frieza states that he had only been fighting at 1% of his full power. Also, no reference is made in this dub to Frieza not using even a third of his power while battling Goku with x10 Kaioken.

After taking another beating, a severely battered Goku attempts to create a giant Spirit Bomb calling on the energies of Namek's solar system as a final resort. Piccolo is able to distract the tyrant long enough, and Goku is eventually able to heavily wound Frieza using the Spirit Bomb.

Believing the warlord to be dead, the heroes take the time to relax, not noticing that Frieza had emerged from the blast's crater, retaliating by mortally wounding Piccolo and murdering Krillin (in a way similar to how Vegeta killed Cui). (In the manga, Frieza intentionally fired at Piccolo, while in the anime, Frieza fired at Goku and then Piccolo pushed him out of the way and took the blast instead.) Already bordering on the edge of his rage, when Frieza threatened Gohan, Goku was pushed over the edge, his rage exploding, causing Frieza to inadvertently create what he had always feared: a Super Saiyan.
Goku endures Frieza's wrath, until Frieza murders Krillin and ignites Goku's transformation into a Super Saiyan.

In the ensuing battle, Super Saiyan Goku and Frieza trade blows, but as the fight progresses, Frieza's 50% power clearly proves to be less than adequate against the Super Saiyan; even his Death Beams at that level have little effect on the newly empowered Saiyan. In frustration, Frieza sends a Death Ball into the core of the planet, starting a chain reaction that would destroy Namek in five minutes (He reveals immediately afterwards that he held back too much of his power for the Death Ball to be a complete success). Frieza unleashes 70% and then 100% of his power. At this point, Frieza launches a terrific assault against Super Saiyan Goku, who had not expected Frieza's power to be as high as it is.

However, Super Saiyan Goku realizes that after sustaining so much damage in his 50% state, Frieza's body would no longer be able to handle his 100% power for very long. Super Saiyan Goku and Frieza face off and eventually after a very long battle, Super Saiyan Goku gets the battle under his control, delivering a final momentous blow to the tyrant that symbolically ends Frieza's reign. Seeing Frieza's power slipping fast now, Super Saiyan Goku decides to call off the fight, claiming it would be pointless to continue, as Frieza is losing strength rapidly and Super Saiyan Goku had already humbled the tyrant. He also mentioned that he was holding back ever since Frieza achieved 100% to see what the form was capable of. Humiliated, Frieza refuses to relent, attacking Super Saiyan Goku with two of his own more powerful versions of the Chasing Destructo Disk. As Super Saiyan Goku dodges the attacks, Frieza ironically becomes distracted long enough to be vivisected by his own attack.

Barely clinging to life but desperate to survive, Frieza begs for mercy, which Super Saiyan Goku hesitantly provides. Frieza's pride refuses to allow him to be beaten and saved by a Saiyan "monkey", and he expends what little energy he has left to attack Super Saiyan Goku. Overcome with anger, Super Saiyan Goku fires a ki blast that consumes both Frieza and his attack and ravages what remains of him in the process. As far as actual events go, this seemingly ended Lord Frieza's reign over the galaxy. As far as the narrative element goes, this ended the true Frieza character that was developed from the beginnings of the series.
[edit] Death
Mecha Frieza is slain by Super Saiyan Future Trunks.

Unbeknownst to Goku and everyone else, Frieza was not killed on Namek. Frieza's shredded body floated in the planet's debris, kept company only by his thoughts of how the universe's conqueror had been thoroughly beaten by a Saiyan. His father, King Cold had crews search the area, not believing his son to have been destroyed by something as insignificant as the explosion of a planet. What could be found of Frieza was salvaged, and reconstructed with cybernetic enhancements. Scarred and bitter. Knowing he was stronger than ever before - Frieza's first thought upon rehabilitation is revenge on those who defeated him on Namek.

Frieza beats Goku to Earth (despite his ill intentions towards Earth and all who lived there, Frieza notes It's a good planet on first viewing) and orders his henchmen to find and slaughter its inhabitants, with Frieza keen on killing his enemy's friends himself. However, his army is torn apart by the blade-wielding fighter Future Trunks. Frieza dismisses his challenger as an insolent child, and pays him almost no heed until the boy reveals himself as another Super Saiyan.

Dumbstruck, Frieza makes several different efforts to kill Future Trunks, each of which is parried easily (Only in the anime. Originally Future Trunks wasted no time and kills Frieza after a single attack). He then plays his trump card in the form of a Death Ball ten times the size of the one that destroyed Planet Namek (this attack is called Supernova in Dragon Ball Z: Budokai Tenkaichi 3). Even this is nonchalantly brushed away, until a mortified Frieza causes it to detonate with another shot of ki. Thinking him dead, both father and son are stunned when Future Trunks fires a Burning Attack out of nowhere. Fuming, Frieza becomes oblivious to his opponent's position, and is surprised and sliced in half by the Saiyan youth before being cut to pieces and vaporized in an effortless blast.

In Trunks and Cell's alternate future, it is implied Goku would have used Instant Transmission to teleport to Earth and kill Frieza and his father King Cold.
[edit] After death
King Cold and Frieza in Hell.

After his death, Frieza makes numerous cameo appearances throughout the remainder of the series from Hell, including observing Goku's fight with Kid Buu alongside other defeated villains from the series. His first (and most major) role was teaming up with Cell and causing trouble in Hell, along with King Cold and the dead members of the Ginyu Force. This was one of the rare times we see Frieza and Cell (two of the three main villains of the show) talking to each other.
Frieza, King Cold, Cell, and the Ginyu Force after being beat down by Pikkon and Goku.

Frieza and King Cold were the only two villains in this scene to not be thrown onto the Mountain of Needles by Pikkon; Pikkon knocked Frieza out with a single punch to the face after elbowing King Cold in the stomach. Then all seven were locked up in a prison cell. Later when Frieza saw Goku winning against Kid Buu via the Spirit Bomb, he remarks "Why am I not surprised?".

In Dragon Ball GT, he teams up with Cell to act as a distraction for Goku while a horde of villains from the Z Fighters' past escape Hell. Frieza traps Goku in the next world, but even allied with Perfect Cell, he is eventually defeated and remains in Hell.
Frieza and Cell appear in Hell.

They work together very well in fighting Goku, almost to the point where they were already on the same page long before Dr. Myuu put his plot in motion. Perhaps their shared hatred for Goku, as well as the fact that Cell (having Frieza's cells in his body) knew what made Frieza tick, caused them to almost form a friendship of sorts.
edit Power level

Frieza's power level in his first form is stated to be 530,000 in the manga. When he transforms into his second form, his power jumps to "over 1,000,000.". In the series, when transforming into his second form, he continues to power up as he fights, only to transform again when outmatched by Piccolo. His power level in his third form is unknown, but his final form has a power level of 12,000,000 at 100% of full power. At 50% power (around 6,000,000), Frieza is able to cope with Goku's Kaio-ken x10, but a Kaio-ken x20 gives him trouble (Goku's 300,000x20=6,000,000 which roughly equals Frieza's 50%). At 100% of power, Frieza is able to battle nearly evenly against Super Saiyan Goku, and even takes a slight advantage. However, because of the power output, his 100% power slowly drains, leading to his defeat.

The RPG game, Legend of the Super Saiyan provides different power levels for Frieza. In his first form, Frieza is at a maximum of 500,000. In his second stage, he is stated to be at 1,000,000, and in his third form his power is 1,500,000. Once reaching his final form, Frieza's power level raises to 3,000,000.
edit Forms and transformations

Over time, Frieza's power became so great that his body could not comfortably contain it, and a series of physical transformations were developed to limit his actual strength. While other beings in Dragon Ball Z transform to increase their power, Frieza transforms to control and contain it. His true form is his fourth form, with each of his other transformations meant to restrict his power and conceal it from his enemies. Frieza even says upon transforming to his second state that he has a harder time controlling himself and his power due to the immensity of his current strength. That would suggest that the second and third forms are mere physical augmentations which would allow Frieza to build enough strength to revert to his true form. While changing shape from his "first-form", each alteration builds on the previous.

In all, Frieza demonstrated four transformed states, each with increasing power (some larger than others and each resulting in different physical attributes). Frieza may also use these transformations to purposely decrease his power in order to torment his opponents by giving them a false sense of hope.