Roger Johnson joined Blues in June 2009 from Cardiff City for a fee of £5m.
The central defender, who was regarded as one of the brightest defensive properties outside the Premier League, put pen-to-paper on a three year deal at St. Andrew's.
Johnson's arrival broke the club transfer record paid for a defender.
The Ashford-born player his career at Wycombe Wanderers and was captain of the side before sealing a move to Cardiff in 2006 for £275,000 after making 183 appearances for the Chairboys.
As well as his defensive strength, Johnson frequently causes opposition defences problems from set-pieces.
The 6ft 3in tall centre half scored five goals for the Bluebirds during the 2008/09 season and was named in the Coca-Cola Championship team of the year following a sustained spell of impressive displays for the Welsh outfit.