Tom Brady told Sports Illustrated‘s Peter King that he recently signed a contract to endorse Under Armour after his deal with Nike expired in the summer. The deal includes a financial stake in the 14-year-old Maryland company.

“Under Armour’s everything I was looking for,” Brady said. “It’s cool. It’s fun. It’s what so many of the kids are wearing, and I like to try to stay cutting-edge. I like the company. I think we’ve got a lot in common. We both want to stay hungry, stay humble.”

King reports that Brady is Under Armour’s first superstar athlete, and the quarterback will appear in commercials and print ads starting in early 2011.

Under Armour’s highest-profile endorsers are Ravens linebacker Ray Lewis, swimmer Michael Phelps and skier Lindsey Vonn.

“At this point in my career, it’s got to be about a product I believe in,” Brady said. “I felt there wasn’t anything better out there. This is such a young company to be where they are. This kind of tells you where the market’s at.”