Prior to his MLB career Teahan attended St. Mary's College, where in 2002 he was drafted in the first round of the MLB Draft by the Oakland Athletics. He was immediately placed with the Athletics' minor league affiliates for his first few years of conditioning.

Still playing in the minors, Teahan was part of a three team trade on June 24, 2004, and was sent to the Kansas City Royals. Following the trade he placed with the Royals' minor league affiliates.

Teahan was called up on April 4, 2005 to make his MLB debut with the Royals. He played a total of 130 games his rookie season, hitting 60 runs and seven homeruns at third base. Teahan joined the Royals for 109 games in 2006, hitting 70 runs and 18 homeruns before surgery to repair a partially torn labrum and partially torn right rotator cuff cut his season short. Despite the injury, Teahan was named the Royals' Player of the Year for the 2006 season.

Teahan returned to the Royals for the 2007 season, moving to right field. He played in 144 games, hitting 78 runs and seven homeruns. He finished the 2007 season with a .285 batting average.

1. Full name: Mark Thomas Teahen
2. Born: September 6, 1981
3. Birthplace: Redlands, California
4. Bats: Left
5. Throws: Right
6. Dual Citizen: Canadian-American