We know the Colts have already interviewed Matt Nagy (off the board), Josh McDaniels, Kris Richard, and Mike Vrabel.
Late yesterday, they surprisingly brought in Baylor head coach Matt Rhule. Today, it's Panthers defensive coordinator Steve Wilks:
Wilks first NFL job was as secondary coach for the Bears team that the Colts defeated in Super Bowl XLI. Since then, he's held the same title with the Chargers and Panthers, before being elevated to defensive coordinator/assistant head coach this past season in Carolina. He would've crossed paths with Chris Ballard during his time in Chicago, as Ballard was a scout for the team in all three of Wilks' seasons (2006-08).
Wilks also interviewed with the Giants, and was reportedly receiving interest from Arizona as well.