Sir Galahad is a Greyhound who works as a Race Dog at the Springfield Downs. He is never seen, but only mentioned. Homer Simpson and Bart Simpson prepare to bet on Whirlwind, a dog Barney Gumble insisted would win. However, Homer is reluctant, and at that moment the loud speaker says Sir Galahad will be replaced with Santa's Little Helper. Homer sees this as a sign to bet on him. Santa's Little Helper completes the race last (by a lot).
Sir Galahad is a references to a mythical knight of the same name. He was a member of King Arthur's Round Table. He was one of three men to reach the Holy Grail.