PASADENA, Calif. - Jim Parsons, who plays tall, nerdy Sheldon on CBS's

The Big Bang Theory

, is no science whiz.

He failed a college science course because he took it for the wrong reason.

"I said I wanted to be a meteorologist because we were living on the Gulf Coast and there were hurricanes," he says over lunch at a restaurant here.

"I realized later on it was the sheer drama of it. I really don't care about studying meteorology. . . . I took it for a science credit, and it's the only time I ever failed a class. . . . I was overwhelmed by the theater I was doing and completely underachieving in studies outside of that. It was pathetic."

Parsons, 34, who resembles the genius he plays on the show, is the veteran of 15 failed pilots. "I like auditioning, very much. I enjoy working on things, getting prepared."

When he read

The Big Bang Theory

, he says, he knew he could play the part.

Parsons got the script the night of the Academy Awards and instead of going to Oscar parties, sat on the floor of his sublet apartment and wrote and rewrote all the lines.

"I knew if I didn't get the part and felt I could've done more, I really couldn't live with myself because I just knew it was a wonderful fit - whether or not they thought so," he says.

Parsons, who was raised in the Houston area, graduated from the University of Houston and worked in local theater before attending graduate school at San Diego / The Old Globe Theater on a scholarship. Then, with his master's degree, he headed for New York.

"I went to do whatever would have me. I'd only done theater up to that point. So I didn't know for sure how the camera would see me, how I would react to being on a stage like that. So the first thing I did was an Off-Broadway show, very quickly then did a lot of commercials and got a little part on

Ed

, had a scene in

Garden State

, then got a pilot and it snowballed."

Commercials for Quiznos and other advertisers kept him solvent for a while. Along with unemployment and a short-term job with a construction company, Parsons managed to make ends meet.

His father was the president of a plumbing supply company and his mother is a first grade teacher. His sister is also a teacher. His father was the humorous one, Parsons says.

He was killed in an auto accident six years ago. "And I still don't know all the ways that changed and affected me, but there's no way it didn't," Parsons says.

"It changed the whole family dynamic. . . . I realized in the end I could only be of use to the family fully if I did what I needed to do and then went on.

"What's funny is I then moved to New York and have a terrible sense of direction - my dad was very good at it - and I understood the city and how to get around so quickly that it boggled my mind. And still, to this day, I think it had something to do with [his death]."

Once he hit L.A. the gift was gone, he says. "Here I just have to MapQuest it and if I get off the path I just have to say, 'I won't be making it today.' "