Riley is a stray mutt in Homeward Bound II: Lost in San Francisco, and the leader of a gang of stray dogs.
Riley is the leader of a gang of street dogs whose names are Delilah, Bando, Sledge, Stokey, and Spike. He is first seen arriving with his gang and saves Shadow, Sassy, and Chance from Ashcan and Pete, two vicious junkyard dogs. He then tells Shadow and Sassy (Chance fled, thinking that Riley's gang were reinforcements for Ashcan and Pete by Sassy) that it is unsafe to be around here because there are humans present, and humans are bad news.
Riley reveals that he hates all humans, as well as pets who associate with humans. The reason why (according to what Delilah told Chance at some point) is that a long time ago, when Riley was just a puppy, he was a Christmas present for a boy. However, the boy refused to like him and play with him, so the parents got rid of him by leaving him in a gutter on that Christmas night in the rain.
Riley later starts to change his mind about humans after Shadow rescues a boy named Tucker from a burning house.