Dr. Sheldon Cooper is Leonard's best friend, roommate, and co-worker at Calech. Sheldon is the smarter of the two with an IQ of 187, but is definitely the more socially awkward of two. He has a ridiculous ego, is extremely stubborn, but the group seems to put up with him.
Sheldon: Why are you crying?
Penny: Because I'm stupid!
Sheldon: Well that's no reason to cry; one cries because one is sad. For example, I cry because others are stupid and it makes me sad.
Penny: Hey, Sheldon, did you change your Wi-Fi password again?
Sheldon: Yes, it's "Penny, get your own Wi-Fi." No spaces.