Mangini's last coaching gig was in 2010, when he was the head coach of the Cleveland Browns. He spent two seasons with the team and went 10-22. Before that, he coached the New York Jets from 2006-08, leading the team to a 23-25 record. After being fired by the Browns, Mangini was a studio analyst for ESPN.
Mangini came up in the Bill Parcells and Bill Belichick coaching trees, and is considered a strong defensive mind. It's a bit unusual to see him take an "offensive consultant" position, although he did serve as an offensive assistant with the Ravens in 1996. It's unknown what kind of role he will serve with the 49ers right now, but fans can rest assured that this is still very much Jim Harbaugh's ship to run.