"Brad, he rubbed a lot of people the wrong way. He was very aggressive," Rick Hendrick said. "But he learned how to control that and how to race, and he did it in a hurry."
And it happened at Penske, where he was paired in the Nationwide Series with Paul Wolfe, who didn't want the job when first approached. He ultimately changed his mind, and the duo won the championship in their first year together.
Wolfe said he wasn't deterred by Keselowski's reputation, and looked only at the talent level and potential.
"I'm kind of the guy that takes it one day at a time, try to be better each and every day at what I do, and never really looked at it from the standpoint of 'I want to go win a championship with him,'" Wolfe said. "It was, 'I want to go win races and continue to grow as a team.' We've done that each and every week and every year."
While things were clicking in the Nationwide Series, Keselowski was struggling in Cup races. So Penske moved Wolfe up in 2011 to Cup, and Keselowski took off, winning three races to make the Chase for the Sprint Cup championship.
It set the pace for this season, the breakthrough year for Roger Penske's first Cup title 40 years after first entering NASCAR.
And it showed that Keselowski has come a very long way in three very short years.
He looks back now at how he behaved, both on and off the track, and understands that coming up with his family's low-budget race team helped mold him into who he is today, even if it gave him a narrow view of the world.
"I think I suffered from some serious confidence issues when I first came into Cup that were a result of mostly just not having the speed to be successful and trying to do too much," he said. "I was trying too hard to be the "I'' in team, and there is none. That's pretty obvious looking back now. But I didn't know that. I do now. It's not until you have a group around you that shows you that you don't have to do all the work, that you can share it, and that as long as you respect them, care about them and work with them, you can be successful. That's something I had to learn on my own.
"I never had anybody teach me that. Nobody ever taught me about teamwork. My family and my parents, my mom and dad, they taught me about work ethic, they taught me what it meant to be a part of a family that had each other's backs, but it's a lot different when you're not family."
But Keselowski is part of the family. The Penske Racing family, and the NASCAR family. He's the champion, and underneath his fancy new clothes is a hardworking blue-collar kid from the suburbs of Detroit who loves NASCAR and wants to do anything he can to promote the sport.
"It's not like the champion is Miss America who goes out to civic organizations and gives speeches or anything like that," said NASCAR analyst Kyle Petty, son of seven-time champion Richard Petty. "He grew up in Michigan. He grew up working on these cars. He's a blue-collar guy from a blue-collar family and when we go back to Dale Earnhardt Sr., David Pearson, 'The King' and to Darrell Waltrip and guys like that, they worked their way up through.
"Brad Keselowski traveled the same road to get to this point. He'll be a great champion for this sport."