His nickname is unique.

After Fresno's Casey Olson won his first mixed martial arts fight, several years ago, his promoters told him he needed a nickname.

He hadn't really thought about it, hadn't considered much beyond the idea of not getting his face dented in, so he went to his roommates. They had lots of ideas, of course, most of them equally masculine and ridiculous.

Fighters have a certain theme to their nicknames, and generally that theme is either: I'm really good, or I'm really tough. Most every name is some variation of that. Randy "The Natural" Couture. (This comes easily to me.) Chuck "The Iceman" Liddell. (Nerves do not affect me because of my unmatched confidence.)

The Pitbull. The Assassin. The Executioner. The Real Deal. Merciless. Macho. You get the idea.

But Olson -- Clovis High graduate, former Fresno City state champion, former Fresno State wrestler, former manager of The Old Spaghetti Factory -- goes by "The Underdog." There is a certain, well, vulnerability to proclaiming yourself an underdog. Fighters aren't supposed to be doubted, to have weaknesses, and they're certainly not supposed to acknowledge them up front.

It was Olson's dad who came up with it. Andy Olson told his son he'd always envisioned him as the underdog, partly because Casey had overcome so many serious injuries in wrestling, and also because they'd dealt with so many family issues.

Truth is, Andy had always envisioned himself as one of life's underdogs. A lot of the obstacles Andy faced were somewhat self-constructed, you might say: his endless debts, and living beyond his income, and his incarceration when his kids were little, and then his three divorces.

Oh, he loved the underdog, though. Casey Olson used to come home after school and there would be a stranger mowing the lawn, and then his dad would give the man a meal, a little money and drive him back to whatever street he'd picked him up on.

"I learned that it's great to give," Casey Olson says, "but if you can't personally take care of yourself, how can you take care of somebody else? I learned that from him, from his mistakes."

Casey Olson and his dad used to talk about how Andy Olson should take better care of himself. His three kids used to call him the fast-food king, joke about how if he wasn't careful he'd die of a heart attack, the way his father had at age 47.

Last Nov. 19, Andy Olson came over to Casey Olson's house to check on his son, to fix Casey's car and go pick up some medicine for him. After he was done, Andy drove to Baird Elementary to referee a wrestling match, had a heart attack and died. He was 53.

"He was my life, my best friend, my father," Casey Olson says. "My dad got me into wrestling. My dad was the one person who supported me all along, the one who backed me when the rest of my family was like, 'What the heck are you doing fighting? You have a job.' "

He was the one who'd given him the perfect nickname. Olson is, after all, the kid who'd walked on at Fresno State and made the NCAA wrestling championships. He is the one who, at 5 feet, 7 inches, and 150 pounds, will inevitably be challenged by a half-drunk fan in public. You're Casey Olson? Yeah, right. At which point Olson invites the guy for a little sparring at a workout the next morning.

No one has showed up yet.

Tonight, Olson will try to move on with his career. He's on the card of the Strikeforce Challengers event at the Save Mart Center, and if it seems like a guy whose MMA record is 11-3 is doing just fine, he's had a long, long year.

He'd had such a great 2008, made more money than he'd ever expected in the sport, kept his great following, got paid $22,000 for a single bout. But then his dad died and he's only taken one fight since, a loss. He and his girlfriend got out of town for quite awhile. He took a job bartending.

The lessons he learned from his father's inspiration and financial troubles have been there, he didn't need some great epiphany to realize them, but the hole was there, too. So was that empty seat in the stands and that useless number in his cell phone. You don't stop needing a dad because you turn 29.

"It's been a tough year," says Casey's brother Michael. "I think [the fight] will be cathartic."

Rooting for an underdog never felt better.