He is a bad tempered, foul mouthed old drunk who draws his sword and pistols at the drop of a hat. Often accusing anyone or anything of plotting to kill him. He has sort of a Jeremy Irons gruffness about him.
Sancho on the other hand is a fat, upbeat and jolly mexican who is always laughing and finding simple things amusing. He loves gambling and loves women. He sticks with Don Quixote because he is a constant source of
entertainment. I had Cheech Marin in mind when sketching him.
Hopefully one day I can expand on this idea more.