In the 1860s, two stray dogs called Bummer and Lazarus were given the run of the city of San Francisco at a time when any other stray dog would have been rounded up and thrown in the pound. But Bummer and Lazarus were different—they were celebrities. The newspapers of the day reported their doggy exploits as if they were Posh and Becks or Brad and Angelina. If they got into a fight with rival dogs, the papers often printed an exaggerated account of it the next day, complete with eyewitness testimony and a dramatized cartoon of the event. Even Mark Twain took time out from working on Huckleberry...

Swansea Jack was a black retriever who lived with his owner William Thomas near the River Tawe in Swansea, Wales, during the 1930s. One day, Jack saw a small boy drowning in the river and ran in, pulling the boy to shore by the scruff of his neck. There was no one around to see it, and had circumstances been different, the boy would probably have spent the rest of his life telling the story to people who would never believe him. But Jack wasn’t done. Within a few weeks, Jack rescued another swimmer, this time with witnesses in attendance. And then another. And another. And so on. Over the...