The 64-year-old has a 62-50 record with the Colts and Lions. He led Indianapolis to a 14-2 record and Super Bowl XLIV appearance in 2009 but lost to the New Orleans Saints.
Indianapolis went 10-6 and fell in the wild-card round the following year. In 2011, quarterback Peyton Manning underwent neck surgery and was forced to miss the entire season. The Colts then dropped to 2-14, and Caldwell was fired.
He wasn't out of work for long as the Baltimore Ravens hired him as the team's quarterbacks coach. Eventually, he was promoted to offensive coordinator, which is the role he held when the team won Super Bowl XLVII against the San Francisco 49ers.
Two seasons later, the Detroit Lions hired him to be their head coach. Caldwell had a successful stint there, going 36-28 and leading the team to the playoffs twice. However, the team went in a different direction after the 2017 season, and Caldwell had been out of work ever since.
Caldwell brings a wealth of experience to Miami. First, he knows a thing or two about bonding with a franchise signal-caller and future Hall of Famer, as he and Manning got along well. Michael Rothstein of ESPN wrote on the topic in 2015, characterizing their connection as a "close relationship."
Manning also credited Caldwell, who was Indianapolis' quarterbacks coach from 2002-2008, with improving his game. "I really felt like I just sort of took a step up during the years that he was my quarterbacks coach," he told Rothstein.
Caldwell also deserves credit for taking the Lions—largely a losing franchise since its inception—to the playoffs twice in four seasons. That isn't an easy task.
Furthermore, he led a team to a Super Bowl berth, which is something few quarterback coaches candidates can claim.
He joins the Dolphins ahead of what could be a transitional period. The team hired Brian Flores as its head coach to replace Adam Gase. This is Flores' first head coaching job, so he can lean on Caldwell to help him with the adjustment.
Miami hasn't committed to keeping Ryan Tannehill for the 2019 season, either. It would save $18.7 million by releasing Tannehill after June 1, with almost $7.9 million counting against the cap in 2019 and $5.6 million in 2020, per Over the Cap.
Especially if the Dolphins turn to a rookie quarterback as their starter, Caldwell's experience could prove invaluable.