The four-time All-Pro spent the last six seasons with Minnesota after four years with Kansas City. He leads the league with 128 1-2 sacks since entering the NFL as a fourth-round draft pick in 2004.
Although the Vikings slumped last season, Allen had a seventh consecutive double-digit sacks season and the eighth overall of his 10-year career. He started all 16 games, making 11 1-2 sacks and 52 tackles. He also had two forced fumbles for Minnesota.
Chicago's defense was one of the NFL's worst in 2013, ranking 30th overall and 32nd and last against the run. Allen also has been a solid run defender during his career.
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