Briscoe, 31, scored a hat-trick on his debut for Rhinos at the start of the 2014 season and, other than through injury, has been a constant in the team ever since, scoring 91 tries in 191 games.
Now settling into a new role at centre, the former winger will line up against his previous club Hull in his benefit match at Headingley on Sunday.
“He has been an exemplary role model for any young professional, his longevity and the quality of his performances,” Agar said of Featherstone-born Briscoe, whose first Hull appearance was in 2008.
“He probably gets missed a little bit, having played in such a good and successful Leeds team, full of iconic players - and probably playing on the other flank to a player as good as Ryan Hall for so long.
“But he represented England against Australia when he was 19 and if you look at the amount of cup finals he’s played in and winner’s medals he’s got - and the fact he won a Lance Todd trophy with a record try haul - it is a remarkable career, stuff you could only really dream of.
“Because he is not a guy who courts too much publicity, he is a very quiet, level-headed, professional, family man, his exploits have not had as much fanfare as other players who have maybe not achieved as much in the game.”
Agar was boss at Hull for part of Briscoe’s time there and hailed him as a pleasure to coach.
He said: “I wouldn’t be aware of any indiscretion from Tommy, anywhere.
“His professionalism is absolutely flawless.
“Along the way he has become a dad three times and educated himself by going to university to the stage where he’s doing a doctorate now.
“It has been an impressive career from a hugely talented, but also very grounded individual.”
Briscoe is noted as a strong ball carrier, but Agar reckons a cool temperament is one of his greatest strengths.
“When he first came through at Hull, he was a kid who not a lot fazed him,” Agar recalled.
“He came from a very strong junior team, with the likes of Liam Watts, Joe Westerman, Richard Owen and Keal Carlile and even then he was under the radar a bit.
“I think Hull FC were the only club to offer him a contract, whereas every club in the game were clamouring over some of the other guys
“I’ll be honest and say we [Hull] thought he had a chance, but did we think his progress would escalate in such a rapid way and he’d end up being a world-class talent at 18/19?
“I would be fibbing if I envisaged that.
“His physical attributes - his power - are good, but also his temperament and composure.”
It has not always been plain sailing for Briscoe, who was sidelined for a year after an anterior cruciate ligament injury in 2019.
“He has had some setbacks, with injury and elements of form,” Agar added.
“But he has always been good enough to ride it through and he is still a very, very good performer at the top level of the game.”
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