Fang
Background
Fang is Hagrid's pet Neapolitan Mastiff. He is a coward.
During the events of Harry Potter and the Sorcerer's Stone (2001)
Harry Potter, Ron Weasley, Hermione Granger and Draco Malfoy go to Hagrid's hut and tell him they know about the Sorceror's Stone. They tell him they think Professor Snape is trying to steal the stone, but Hagrid tells them he is one of the professors protecting it. As they are talking to Hagrid, Fang starts sniffing Ron's face. Hagrid pulls out a dragon egg, which hatches into a Norwegian Ridgeback dragon, which Hagrid names Norbert. After they are given detention they are brought by Mr Filch to help Hagrid in the Dark Forest. Hagrid tells them Albus Dumbledore made him send Norbert to Romania. They follow Hagrid and Fang into the forest and find unicorn blood and Hagrid tells them he found one dead a few weeks ago and their goal is to find the wounded unicorn. They split up and Harry and Draco go with Fang. They come across a robed figure hunched over the wounded unicorn and Fang and Draco run away, leaving Harry.
During the events of Harry Potter and the Chamber of Secrets (2002)
Harry, Ron and Fang follow a group of spiders into the Dark Forest. They come to a clearing surrounded by large trees and Aragog comes out of his hole in the ground. Aragog tells them Hagrid didn't open the Chamber of Secrets and the creature that killed the student is an ancient creature spiders fear. After telling them the student died in the girl's restroom, Aragog tells them his children need to feed and as they are surrounded, the Ford Anglia drives up and saves them. After the Ford Anglia makes it out of the Dark Forest, Harry, Ron and Fang get out and the Ford Anglia drives back into the forest.
During the events of Harry Potter and the Order of the Phoenix (2007)
Harry, Hermione and Ron run to Hagrid's cabin and an injured Hagrid tells them Dumbledore sent him to try and get the giants on their side and then feeds Fang the steak he was using to stop his wounds from swelling.
During the events of Harry Potter and the Half-Blood Prince (2009)
After Aragog dies, Hagrid, Harry and Professor Horace Slughorn go inside Hagrid's hut and sing songs and drink as Fang howls.