Lewis was an undrafted free agent in 2011 from Arizona State University who played in eight games last season - three for the Cowboys and five more for the Buccaneers. Over those eight games, he recorded five tackles, an interception and a pass defensed. He also picked up five kickoff returns for 106 yards, so he carries a little value there.
The Bears have a crowded defensive backfield with Pro Bowlers Charles Tillman and Tim Jennings, as well as Kelvin Hayden under contract and expecting Sherrick McManis back off injured reserve, so this move is likely a competition move, especially if DJ Moore finds himself out of Chicago and Zackary Bowman re-working his way into the hearts of Bears fans (and management).
In college, Lewis recorded 26 tackles in his senior season including two for loss, four pass breakups, a fumble recovery and interception; he was also a great special-teamer, returning a kick for a touchdown as well as blocking a kick. He converted to wide receiver a couple times in his career before settling in at cornerback.