Andy Powell - a former Wales international and British and Irish Lion - has retired from rugby.
Having started his career with Newport, the 35-year-old, who won 23 caps for his country, became something of a journeyman, playing for the likes of Cardiff Blues, Wasps and Sale Sharks.
He also had a brief stint in rugby league where he turned out for Wigan Warriors.
Powell, who helped Merthyr win promotion to the Premiership last season, was selected for the British and Irish Lions' tour to South Africa in 2009 but did not make an appearance.
Merthyr chairman Peter Morgan said: "To all Merthyr Supporters I bring sad news, our former captain Andy Powell has decided to hang up his boots.
"Andy's found it hard to get over his current knee injury and will not be forgotten.
"Andy had plenty of time for everyone he will be sadly missed on the field and off."
Powell made national headlines in 2010 when he was charged with drink driving after allegedly taking and driving a golf buggy down the M4 motorway.