Buckbeak is in the third and fourth book at the end of book three he and Sirius -Harry's godfather- both escape together and is briefly in book four when Harry, Ron and Hermione go to vist Sirius. The reason for Buckbeak going on the run is that during the first lesson of Care for Magical Creatures Hagrid took they were going to look after Hippogriffs. As Hagrid explained that Hippogriff are very proud creatures and are very easily affended Malfoy, Crabbe and Golye were not listening and when took over Buckbeak Malfoy called Buckbeak a "great ugly brute" and Buckbeak slashed open Malfoy's arm and of course he over reacted saying that he could not use it for three months and were his father Luicius threatened the Committee of the disposal of Magical Creatures and were forced to execute him, but with the use of the time turner which Hermione used to get to all her lessons, Harry and Hermione went back in time and managed to save both Buckbeak and Sirius. Buckbeak is grey in colour and enjoys the company of Hagrid.