Who was Sir Galahad in Sonic and the Black Knight?

There's a little bit of a mix-up here! Sir Galahad is a character from Arthurian legend, not from the Sonic the Hedgehog franchise.

While Sonic and the Black Knight does feature Arthurian themes, there is no character named Sir Galahad in the game. The main characters are Sonic, King Arthur, and the villain, Merlina the Sorceress.

Perhaps you're thinking of a different character or game?