Tommy Bowe - Ulster/Ospreys
Possibly the most glaring omission from our first list, Tommy Bowe is the top try-scorer in the history of the GUINNESS PRO12.
In two spells at Ulster, either side of a successful four-year stint with the Ospreys, Bowe has racked up 62 tries, which puts him four clear at the top of the all-time standings.
In 2005-6 he was the top try-scorer as Ulster won the title, while he also scored the first try in the Ospreys' 2010 final win over Leinster.
Alun Wyn Jones - Ospreys
Few people have embodied the Ospreys more over the last decade than second row Alun Wyn Jones, the heart of their pack. Since making his debut back in 2005, he has made double figure appearances in the Pro12 season ever year with the exception 2007-8.
A British & Irish Lion captain and Wales' most capped lock, Jones is the real leader at the Ospreys, where he has won three Celtic League titles.
Tim Visser - Edinburgh
Tommy Bowe might be top of the try-scoring charts in the Celtic League, but Tim Visser was very close to overhauling him in a remarkably prolific spell in Edinburgh.
In his first four seasons in the Scottish capital he managed 10, 14, 13 and 11 tries, finishing as the league's top try-scorer in all four years.
His efforts were rewarded when he was named Player of the Year in 2011-12, and unsurprisingly the Dutch-born winger also earned international recognition with Scotland as a result of his Celtic League exploits.
Leonardo Ghiraldini - Benetton Treviso
Italian rugby has traditionally been known for its forward play, and few typify that more than Azzurri and former Treviso hooker Leonardo Ghiraldini.
The 31-year-old spent five seasons with the Italian team, and was one of the key players on their arrival into Celtic rugby.
With Ghiraldini leading the way, Treviso enjoyed some of their greatest success, notably with a seventh-place finish in 2012-13.
His performances with Treviso also led to him becoming Azzurri captain in 2010 in the absence of Sergio Parisse.
David Wallace - Munster
Others at Munster might have achieved greater recognition, but few were as influential as back row master Wallace.
A Munsterman through and through, Wallace spent 15 years at Thomond Park, winning three Celtic League titles along the way, as well as a couple of European titles.
Wallace made 83 appearances in all for the Irish province in the Celtic League, and was one of the best opensides in Europe for the best part of a decade.
Martyn Williams - Cardiff Blues
One of David Wallace's main rivals for the title of Europe's best openside, Martyn Williams was a mainstay of the Cardiff Blues back row for more than a decade.
With Sam Warburton succeeding him, the Blues have not been short of quality at the openside position.
Something of a throwback, Williams was a true linkman in the back row, and racked up 93 appearances for the Blues in the Celtic League.
DTH van der Merwe - Glasgow Warriors/Scarlets
Born in South Africa and then a multiple title winner in Canada, Daniel Tailliferre Hauman van der Merwe has had a more unusual path to the Celtic League than most.
Better known as DTH, he arrived in Glasgow in 2009, and has been one of the most prolific players in the competition ever since.
With 35 tries in six seasons, he was Glasgow's most lethal finisher, and the Canadian international even managed a try in last year's GUINNESS PRO12 final as the Warriors collected their first title.
Now a Scarlet, he's managed six tries already since coming back from the World Cup, as the Welsh side challenge for a play-off spot.
Dries van Schalkwyk - Zebre
The player who has spent the least time in the tournament on our list, but few have made more of an impact in Zebre's short existence.
The powerful No.8 arrived from South Africa in 2012-13 and has quickly established himself as one of Zebre's most influential players.
A dynamic ball-carrier, Van Schalkwyk has managed 15 tries in just four seasons, a fine return for a back rower.
This season Van Schalkwyk has crossed the line six times, making him the most prolific forward in the competition, and has been rewarded with an Italy call-up having qualified on residency.
Felipe Contepomi - Leinster
Leinster have had their share of influential overseas players, from Rocky Elsom's sensational one-season stint to current captain Isa Nacewa's long-term impact.
But few can match Felipe Contepomi, the Pumas legend who joined in 2003. A qualified doctor, Contepomi racked up 877 points in the Celtic League, putting him fifth on the all-time records list despite playing only six seasons in Dublin.
He led the league for points in two of those seasons, and as a playmaker he is one of the very best to have graced the league.
Regan King - Scarlets
Talking of influential imports, there have not been many more impressive than Regan King.
The former All Black centre has been at the heart of the Scarlets' entertaining, ambitious style over two separate spells.
With 22 tries in 117 appearances he has played his part on the pitch, but his influence off it goes even further.
He also made history earlier this season when he played alongside son Jacob Cowley, the first father-son duo ever to do so in the GUINNESS PRO12.
Michael Swift - Connacht
Connacht might be enjoying their most successful season in recent times, but over the previous 15 years, lock Michael Swift was the heartbeat of the side.
The all-time appearance leader until he was overtaken by teammate John Muldoon, Swift now sits third in the standings.
After bowing out at the end of last season, it would be cruel on Swift if Connacht were to win a title in the first season after his departure, but there is no doubt that he played his role in getting the Galway province to where they are today.
John Barclay - Glasgow Warriors/Scarlets
When it comes to back rowers, Scotland have produced a whole host of top quality operators, and over the last ten years few have done more than John Barclay.
168 Celtic League appearances with the Glasgow Warriors and then the Scarlets speaks for itself. During his nine seasons with the Warriors he was also a regular on the international stage, but after falling out of favour at Test level he has been a sensational pick-up for the Scarlets.
Eventually those performances were rewarded though, and he is back in the Scotland set-up and scoring tries for Vern Cotter's side.
Michael Owen - Pontypridd/Newport Gwent Dragons
A hugely influential player with both Pontypridd and the Newport Gwent Dragons, Michael Owen was also the man who captained Wales to their first Grand Slam in 27 years.
Best known for his handling skills, Owen racked up 73 appearances in all in the Celtic League including a five-year stint in Newport.
Along with coach Paul Turner, Owen was a very important player for the Dragons during his time at Rodney Parade.
Ronan O'Gara - Munster
Few half-back pairings have been more synonymous with a province than that of Ronan O'Gara and Peter Stringer, who pulled the strings both domestically and at international level for over a decade.
O'Gara played his entire career at Thomond Park, eventually retiring at the end of the 2012-13 season, and helped the province to three Celtic League titles, including a Grand Final victory over rivals Leinster in 2011.
Best known for his tactical kicking, at his peak O'Gara was one of the very best at playing the game in the right areas.
Nick Williams - Munster/Aironi/Ulster/Cardiff Blues
When it comes to making an impact across the Celtic League, Nick Williams stands out. The giant No.8 began his time in Europe with Munster before playing an important role for Aironi, the predecessors to Zebre.
A move to Ulster saw him enjoy huge success, including a Player of the Year award in 2012-13 when Ulster reached the final.
Next season he will discover yet another country and GUINNESS PRO12 club when he moves to the Cardiff Blues.
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