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: I'm a Sagittarius, which probably tells you way more than you need to know.
Sheldon: Yes, it tells us that you participate in the mass cultural delusion that the sun's apparent position relative to arbitrarily defined constellations at the time of your birth somehow affects your personality.
Penny: Participate in the what?
Sheldon: Why on earth are you telling me all this?
Leonard: Sometimes you movements are so lifelike I forget you're not a real boy.