Date of birth: 24 November 1970
Nationality: German
Playing career: VfL Wangen, VfB Stuttgart (twice), TSV 1860 München, VfL Wolfsburg, 1. FC Köln, Eintracht Frankfurt
Coaching career: VfB Stuttgart (youth), VfB Stuttgart, FC Schalke 04 (youth), FC Schalke 04

• Having risen through Stuttgart's youth department, Keller made his first and only Bundesliga appearance in 1990 before leaving for third-tier 1860 München, where he helped the club to win promotion to the second and then first divisions.

• A fringe player in the Bundesliga, he moved to second division Wolfsburg and again won promotion, subsequently becoming a top-flight regular and earning a return to Stuttgart, where he played in the 1998/99 UEFA Cup.

• Joined Köln in 2000 but relegated two years later, prompting a switch to Eintracht, whom he helped into the Bundesliga only to miss most of the season with cartilage damage; relegation and further injury problems led to retirement in 2005.

• Took over Stuttgart's Under-19 side in 2008/09 and became Christian Gross's assistant with the first team in December 2009; the following October, replaced Gross as head coach but lasted only two months before making way for Bruno Labbadia, although Keller continued to work for the club as a scout.

• Appointed Schalke's U17 coach in summer 2012, on 16 December that year he stepped up to the senior side following Huub Stevens' departure.