He has become the poster boy for the new-found aggression feeding into the Blues' forward pack but New South Wales captain Paul Gallen is confident David Klemmer will keep his cool in Wednesday night's Origin decider at Suncorp Stadium.

Describing the finale to the 2015 Holden State of Origin Series as the "biggest game in history" and the most important game of his career, Gallen knows that discipline and aggression must be measured in equal doses in such an intense arena.

Klemmer ripped into the Queensland pack in his second stint in Game Two with unbridled ferocity, but has conceded just the lone penalty in his first two Origin games for the Blues, his skipper backing him to keep his bizarre off-field antics well away from the playing surface.

"'Klem' will keep a lid on it," Gallen said on the eve of the match.

"He's got a bit of a reputation amongst you guys [the media] as being a bit of lunatic and let me tell you, away from the field he is. He's nuts. Some of his behaviours in the hallway are funny but he gets on the footy field and he's really, really mature.

"He listens to everything, he wants to learn, he trains really, really hard so once he's on the field he's as mature as anyone.

"He's not one of these blokes who will lose his head and start throwing punches and give silly penalties away. He's a good, mature young kid and he'll be fine."

As the team took to Suncorp Stadium for their final captain's run on Tuesday morning, Klemmer cut a relaxed figure as he warmed up, the enormity of the occasion appearing to wash over his broad young shoulders.

His perceived lack of respect for Maroon veterans Cameron Smith and Corey Parker has ruffled some feathers north of the border, Gallen surprised a 21-year-old giant in his first Origin campaign has managed to attract so much attention.

"He has got under their skin that's for sure," said Gallen ahead of his 20th Origin appearance for the Blues.

"You don't see Queensland talking about NSW too much and they've definitely spoken about guys like him and [Michael] Ennis.

"He's a big, powerful strong thing and I wouldn't want him running at me the way he runs at them. I'm sure they'll be wary of him."

This article first appeared on NRL.com