John Joseph Hannahan IV, who goes by Jack, was born on March 4, 1980 in St. Paul, Minnesota. He is the third baseman for the Oakland As.

Jack is 6' 2", weighs 205 pounds, bats left and throws right.

College
Kack attended the University of Minnesota.

Minor leagues
Jack was drafted by the Detroit Tigers in the 3rd Round of the 2001 MLB Draft.

Jack made his major league debut on May 26, 2006, playing first base. He only appeared in a couple of games, however, and would spend all of 2007 in the minors.

On August 13, 2007, he was traded to the Oakland Athletics for outfielder Jason Perry.

The Athletics purchased his contract the next day.

Major Leagues
On August 15, 2007, Hannahan got his first major league hit, a double, off Mark Buehrle of the Chicago White Sox. It was the 14th major league at bat of his career. On August 20, 2007, against the Toronto Blue Jays, he hit his first career home run off Shaun Marcum.