In Rat-A-Tat Father's Day special, Major's father died in a plane explosion, so Major moved in with Colonel and Don. He used to walk on all fours but now he walks on two legs.
His full name is Major Saab.
Like the other main characters, Major dies and is revived repeatedly in many episodes. He was first shown as a greedy dog who can't get enough food. Later on, Major learned to use firearms.