"Coach Childress has stepped away from his role as head coach of The Atlanta Legends," AAF head of football operations J.K. McKay said in a statement (h/t ESPN.com). "We are grateful for his leadership, contribution to building The Alliance, and wish him well in his next endeavour."
The Legends turned to Kevin Coyle as their replacement head coach before the league begins its inaugural season on Feb. 9.
Childress was the head coach of the Vikings from 2006 until 2010, when he was fired after Week 11. He went 39-35 with two NFC North titles and reached the NFC Championship Game during the 2009 season with Brett Favre as his quarterback and Adrian Peterson as his running back.
He was also the offensive coordinator for the Philadelphia Eagles before taking the Vikings job and was most recently the offensive coordinator for the Kansas City Chiefs in 2016.
Eric Mandel of the Atlanta Business Chronicle noted Childress was "a lynchpin to many of the team's major additions" and pointed to his influence in hiring Michael Vick as the offensive coordinator and Jen Welter, the first female coach in NFL history, as a defensive specialist.
Mandel noted former Georgia Bulldogs quarterback Aaron Murray previously cited Childress as the primary reason he joined the AAF as the signal-caller for the Legends.
As for Coyle, he was the defensive coordinator for the Miami Dolphins from 2012 through 2015 and was most recently a defensive analyst for LSU in 2018.