The regal Mufasa, given life by the booming voice of James Earl Jones.
The Encyclopedia of Walt Disney's Animated Characters: From Mickey Mouse to Hercules by
John Grant

Walt Disney Character Description of Mufasa from "The Lion King" (1994)

With his great orange mane and his powerful physique, the first of the movie's two Lion Kings, Simba's father appears much as we might expect him to, and he is voiced appropriately in the deep tones of James Earl Jones. In a way, after the initial scene where Rafiki is presenting the new cub to the massed animals, we see Mufasa only from the viewpoint of the young Simba; he is not so much large as huge, and we have the feeling that he is the ruler not just of the Pride Lands but of the world. This feeling is reinforced by a selection of dialogue in which Mufasa tries to give his young son some idea of the responsibilities of kingship:

Mufasa: Look, Simba. Everything the light touches is our kingdom,
Simba: Wow.
Mufasa: A king's time as ruler rises and falls like the sun. One day, Simba, the sun will set on my time here and will rise with you as the new king.
Simba: And this will all be mine?
Mufasa: Everything.
Simba: Everything the light touches.

"Everything the light touches" would seem to imply the entire world, but immediately we are informed by Mufasa that all kingdoms have their boundaries:

Simba: What about that shadowy place?
Mufasa: That's beyond our borders. You must never go there, Simba.
Simba: But I thought a king can do whatever he wants.
Mufasa: Oh, there's more to being king than getting your way all the time.
Simba: There's more?
Mufasa: Simba, everything you see exists together in a delicate balance. As king, you need to understand that balance, and respect all the creatures, from the crawling ant to the leaping antelope.

Thus are set out the three major themes of the movie. First, obviously, that with power comes duty: kingship is not something that can merely be enjoyed as a privilege but carries a burden of responsibility with it. Second, that any monarchy is confined to its own proper region. And, third, that there is a "circle of life" to which all of the animals belong, from those (like the lions) who are at the top of the food chain to the humblest of creatures. Mufasa expands:

Simba: But, Dad, don't we eat the antelope?
Mufasa: Yes, Simba, but let me explain. When we die, our bodies become the grass and the antelope eat the grass. And so we are all connected in the great circle of life.

This is a point that is hammered home on several occasions throughout the movie, although Disney may have received the occasional letter from an angry antelope.
There is another moral lesson that Mufasa teaches Simba - although it will be a long time later, and only after the intervention of Nala and Rafiki, before the lesson makes itself heard. Mufasa has just rescued the two cubs, Simba and Nala, from the hyenas in the Elephant Graveyard and has led Simba away for a strict paternal talking to:

Mufasa: You deliberately disobeyed me. And, what's worse, you put Nala in danger.
Simba: I was just trying to be brave like you.
Mufasa: I'm only brave when I have to be. Simba, being brave doesn't mean you go looking for trouble.
Simba: But you're not scared of anything.
Mufasa: I was today.
Simba: You were?
Mufasa: Yes. I though I might lose you.
Simba: Oh. I guess even kings gets scared, huh?

Just before this sequence, which becomes one that shows Mufasa is not as straitlaced as his customary majesterial bearing might suggest - rather than continuing to be severe with the cub he ends up romping around with him in a mock fight - there is one particularly effective visual. Simba, following in the trail of his father and expecting Real Trouble, puts his own paw into one of Mufasa's pawprints. The difference in size is spectacular. What is conveyed to us is not just the obvious physical disparity but that Simba, who has earlier been cheerfully boasting about his inheritance, has a long way to go yet before he learns to be a true heir.
But after the play there is more somberness. Mufasa has something to teach his son, and it is the greatest piece of mythmaking in the movie's screenplay. This has been taught to Mufasa by his father (and, it is implied, has been passed down over many generations): the great Lion Kings of the past "look down on us" from the stars in the night sky.
In terms of straightforward action, Mufasa's peak is his rescuing of the young Simba from a herd of stampeding wildebeest, followed immediately afterward by his own murder at the paws of Scar, but there is a much more significant episode later on. Rafiki, having uncovered the grown Simba in the country beyond the Pride Lands, is trying to persuade him that it is his obligation to take up his kingship. The baboon tells the younger lion that his father is still alive, and makes him look into still water by way of demonstration: Mufasa is still alive in that he lives on in Simba. Simba rejects the moral, but then - in a twisted form of scenes in Shakespeare's Hamlet - is visited by an apparition of his father.

Mufasa: Simba.
Simba: Father?
Mufasa: Simba, you have forgotten me.
Simba: No. How could I?
Mufasa: You have forgotten who you are, and so forgotten me. Look inside yourself, Simba. You are more than what you have become. You must take your place in the circle of life.
Simba: How can I go back? I'm not who I used to be.
Mufasa: Remember who you are. You are my son and the one true king. Remember who you are...

The short sequence packs a punch, and it is only on the way home from the movies that one begins to think that if Simba is no longer worthy of kingship, why is he "the one true king"?
Mufasa, spending some great quality time with his young son, Simba.