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.
Penny: Hey, Sheldon, did you change your Wi-Fi password again?
Sheldon: Yes, it's "Penny, get your own Wi-Fi." No spaces.
Sheldon: Why do you have the Chinese character for "soup" tattooed on your right buttock?
Penny: It's not "soup," it's "courage."
Sheldon: No it isn't. But I suppose it does take courage to demonstrate that kind of commitment to soup.
Penny: How'd you see it? You said you wouldn't look.
Sheldon: Sorry. As I told you, the hero always peeks.