Right after graduating from the theatre arts program at SF State in 1999, Patrick Celtic O’Sullivan began his professional career immediately, when he landed a job — at the Olive Garden.

O’Sullivan, 33, was joking, but this sense of humor is what has led him to where he is today. He was, in fact, acting after graduation, but the term “professional acting” is something he said is open to interpretation.

Looking back, O’Sullivan doesn’t really know what inspired him to get into the field. What he does know is that he demanded attention and always looked for the spotlight.

“I wasn’t a theater kid growing up. I was a class clown,” O’Sullivan said.

From being an athlete to a singer in a rock band, O’Sullivan has always played a role — so to speak.

“I’ve been acting up all my life,” he said. “I was not a well-behaved child, but I was always driven to make my classmates laugh.”

Now, 13 years after graduating, O’Sullivan said that this is just the beginning of his 16-year career. Recently he was cast in a role as the goofy alien neighbor, Johnny Unitas, on the brand new ABC series “The Neighbors.” He also portrayed the cop sidekick, Cooper, in the horror film “Smiley,” which was released earlier this month.

“Until this year, I’d been out of the audition game for quite a while, like six years,” O’Sullivan said. “It was an immense confidence builder that all the things I had been doing were about to pay off.”

O’Sullivan wasn’t exactly absent from the scene during his six-year hiatus. He took to acting with an entrepreneurial approach, building his own brand of comedy with an improv sketch show “All About Walken,” an entire theatrical adventure dedicated to the life of actor Christopher Walken.

Remembering his days at SF State, he said the idea for “All About Walken” spawned from making fun of a classmate who did Walken impersonations. O’Sullivan and his friends then began doing the impersonations on a regular basis in the school hallways and at parties.

“My friend Dan Carlos was the first of us to do the impression and later on our pal Amy Kelly started doing it too,” he said. “I started thinking how cool it would be to create a sketch show based on Walken’s life with impersonators of different genders, races and ages.”

O’Sullivan brought this idea to life in a small theater in Hollywood in 2006. He writes, produces, directs and stars in the live performance that has toured from Northern Caifornia to New York City. After the long run, “All About Walken” celebrated its sixth anniversary with a celebratory performance Oct. 15 in Hollywood.

“‘All About Walken’ is like the child I never had,” O’Sullivan said. “It is really the backbone of everything I do and I am floored by the cast’s dedication through the years.”

Kelly, longtime friend and cast member of “All About Walken,” calls O’Sullivan “the most driven, quick-witted, talented and hardest working guy in Hollywood,” and has been since they met at SF State.

“He has taken me many places since then,” the 38-year-old actress said. “He is fearless, and I don’t think that his mind ever stops working. … He knows what makes people laugh and his formula works, and though he is ambitious, he balances it with a good, honest heart.”

Kelly also said O’Sullivan’s creativity made it possible for an entire show, that is quite literally all about Walken, to be so engaging and entertaining.

“Pat worked himself to the bone to put it out there and he made it work,” Kelly said. “People know about the show and they agree that it’s a unique really funny experience. There is a cult following. (There are) people that come every time we perform; they love it!”

Conroe Brooks, O’Sullivan’s friend of 15 years, added that there is no difference between the actor on camera and onstage.

“I think he’s a great actor, a very funny guy,” Brooks said. “(He) is definitely someone you remember.”

Brooks remembers what attracted him to O’Sullivan’s acting was when they first met.

“He was imitating Michael Jackson in the hallway (at school) and something told me this was a cool dude,” Brooks said.

After all his efforts, O’Sullivan works to enliven and inspire, Kelly said.

“If the world were ending tomorrow, Pat would find a way to make you laugh about it. I love that guy and I plan to work with him for the rest of my life,” Kelly said.

O’Sullivan doesn’t know exactly what is in store for his future in acting, but he said he is on track. His career is just taking off.

“The fact that I am finally getting some auditions puts me at the starting line, at last,” he said. “I look back at all the years of preparation and now I know that I am ready — to prove people wrong of course. That’s a big part of what keeps me going.”