Mike is a super mechanic. He never asked questions about the burns that slagged a hole in the front hatch or the claw marks that ruined both doors. You can’t pay for service like that.— Dresden
Mike is a lean man with shaggy gray hair, a black beard, and has looked like he has been in his mid-fifties by thirty and just stayed that way. He is the proprietor of Mad Mike's Motorcycle and Volkswagen Repair in Chicago and once claimed he could "build a Bug from raw steel if I had to".
Harry Dresden describes him as a miracle worker, keeping the Blue Beetle running "eight or nine days in ten", and never asking questions. Mike seems to actively ignore the magical world, preferring a rational explanation to the Beetle's damage to the truthful answer.
In the series
In Storm Front, Mike is mentioned as the mechanic responsible for repairing the damages inflicted upon Harry Dresden's Blue Beetle. When the car breaks down outside Bianca St. Claire's mansion, Dresden has the guard get in touch with Mike's preferred wrecker.
In Fool Moon, Harry Dresden states that he drives a VW bug because Mike declared it as the easiest car in the world to repair. Dresden uses a pair of coveralls with the name "Mike" on it that he'd left in the trunk of the Blue Beetle as a disguise for sneaking into the police station.
In "Mike", Mike Atagi admits that he'd be able to build a Volkswagen Bug from raw steel if necessary, but he only offers to Dresden a choice of two out of three among "cheap, fast and good".