Plaid Cymru AM Rhodri Glyn Thomas has said he will stand down at the next Assembly election in 2016.
He has been the Assembly Member for Camarthen East & Dinefwr since 1999, and is one of only 20 AMs who served in the first Assembly that continue to serve in today's law-making Assembly.
He was Heritage Minister in the One Wales government, but stood down in 2008 after he was caught breaking the smoking ban.
He is currently Plaid's spokesperson on Europe, Local Government, Housing and Transport.
His party's leader, Leanne Wood, paid tribute to him as "a formidable force in Welsh politics."
Plaid Cymru has criticised comments by Shadow Welsh Secretary Owen Smith about the future of devolution in tonight's Face to Face programme. Mr Smith says there should be joint decision-making by Wales and England in important areas like Higher Education funding and social care.
But Plaid's Rhodri Glyn Thomas claims the remarks show there's still an anti-devolution strain in the Labour party.
At the party's weekly presser, Plaid's Rhodri Glyn Thomas AM called for a clear statement from all members of the Assembly on Trident. This, ahead of Plaid's debate in plenary tomorrow which opposes the siting of Trident or any other nuclear weapons in Milford Haven or elsewhere in Wales.
Mr Glyn Thomas said that he didn't want to see any weapons of mass destruction in Wales and wanted to see cross party opposition to the idea. Plaid Cymru is also calling on the UK Government not to replace Trident but to use the resources saved to create jobs.
The debate may well be curtailed, though, because of an amendment from Jane Hutt AM which notes that the Welsh Government has no powers to determine the siting of nuclear weapons and recognises this is a matter for the UK Government.
Andy Richards , leader of Unite ,had described Plaid's call for a coalition of left wing groups to challenge austerity measures " a publicity stunt "
But Plaid Cymru AM Rhodri Glyn Thomas hit back accusing Mr Richards of putting his own political interests above those of his members.
The Am went on further to say