A wonderful servant to Glamorgan, Cosker is the only member of the current squad to have played a part in the club's County Championship success in 1997.
It was Cosker who claimed the final wicket of that campaign as Glamorgan defeated Somerset at Taunton.
The left-arm spinner formed a wonderful partnership with fellow slow bowler Robert Croft prior to the latter's retirement at the end of 2012.
A tourist with England A on numerous occasions, Cosker first represented Glamorgan in 1996 and has featured regularly ever since.
His most profitable season to date came in 2010 - his benefit year - when he claimed 51 first-class scalps at an average of 22.
Cosker picked up a further 49 wickets the following year and although he only mustered 16 in 2012 that still took him past the 500 mark in first-class cricket.