Koroisau created headlines in October when laughed at the suggestion of winning a title at the wooden spooners in the hours after Penrith's premiership success.
Panthers teammates also drew the ire of Tigers fans in the aftermath of the grand final, as they joked that the hooker would never again win a premiership ring.
The issue prompted a please explain from the Tigers, who reached out to Koroisau's management for answers before he began his three-year deal.
Five months later, and Koroisau has done enough to be named as the club's next captain after his appointment was confirmed on Monday night.
"In the short time he's been with us, Api has demonstrated and embraced our core values as a club," chief executive Justin Pascoe said.
"His leadership on the field is vitally important, as is what he does in other areas of our business.
"I think it's a tremendous appointment and I'm sure he will thrive with the added responsibility."
Koroisau insisted after the jibe that he had simply made a poor joke, and was hopeful his on-field skills would win over Tigers fans.
The 30-year-old's rise to the leadership role is his first full-time sole captaincy appointment in his nine seasons in the NRL.
"To be asked to lead this team in my first year at the club, means a lot," Koroisau said.
"This is a terrific group of players, and I am honoured to be their captain.
"From the moment I joined this club, my family and I have been made to feel so welcome.
"It's been a great start to my time as a Wests Tigers player and I look forward to helping this team and this club be the best it can be."
His appointment also comes after the Tigers opted to go from having five captains last year under Michael Maguire to one this season with Tim Sheens in charge as coach.
Adam Doueihi, Luke Brooks, and Ken Maumalo all remain in the Tigers' squad from last year's leadership group, with James Tamou and Tyrone Peachey both let go.
"We have several very capable leaders in this team, and Api is one of them," Sheens said.
"He is very well respected within the group, and I know he'll do a great job."
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