Dennis Creevey is the younger brother of Colin Creevey. He is introduced in the books in Prisoner of Azkaban, and he also joins Dumbledore’s Army in his second year. While his older brother, Colin, is in the movies, he is not. This makes sense as Dennis is never really central
to the plot and his presence isn't really needed. However, it is rather sad that he’s left out seeing as he is a heroic character who fights in the Battle of Hogwarts and who sees his brother lose his life in that battle.