King was the Rams' fourth-round draft pick in 2008 and played the past four seasons in St. Louis. He started 19 games and recorded 131 tackles with the Rams.
His best season came in 2011. King finished with a career-high 63 tackles and recorded the first sack, interception and forced fumble as a pro player.
King was a first-team all-Big Ten selection at Penn State, where he started 31 games. King had 90 tackles and three interceptions in college and also rushed for 227 yards and caught two TD passes.