He'd had a few incidents, on and off the field - the kind that can lead to a downward spiral. But now Luke is co-captain of the Kiwis, and a leader in every sense of the word. It's been some transformation, and Luke credits a stern talk from Kiwis coach Stephen Kearney as the catalyst.
This time four years ago, Luke's reputation was at its lowest point. In a match against England in the 2011 Tri-Nations, he tried to break an opponent's leg; and not just any player, but his cousin Rangi Chase.
It was a horrible incident, and worse when he admitted his intent after the game, saying that he "saw red" before the act. Those comments - and the sickening nature of the incident - attracted global media attention.
It wasn't a good time for the Kiwis, or Luke. "I reacted to that and shouldn't have reacted," says Luke of the episode, prompted by Chase's defection to England. "I should have moved on with my job. I had a job on the field."
Luke took a two-match ban into the off season, and also Kearney's words ringing in his ears.
"Really, if I look back now, that is where the transition started, from being a little shit to where I am now.
"I got a heads up from Mooks [Kearney]. He told me how it was and where I stood. I always respect that he did that [and] from then on it's been going all right."
He says Kearney has been a massive influence, as has Rabbitohs coach Michael Maguire.
Kearney says he could see the talent but wondered if he would last.
"I've seen very talented individuals come in quick and blow out quick.
"In this business, sometimes it's not [just] playing ability that gets you through. You have to get the whole process right. He was a rough diamond and that went on for a few years."
Thankfully, Luke turned the corner and has been a revelation on this tour. He has, with one exception after the first test, dealt well with the media demands. He is one of the most popular players among the British press.
He is also usually, with Roger Tuivasa-Sheck, the last player to leave public training sessions, always ready to sign one more autograph, hold one more baby or smile for another selfie.
Luke didn't play well in the first test as the English forwards monstered their opposites. But he gave a man-of the match display in London. Aside from his dummy half work and defending in the middle of the ruck, his kicking in general play constantly turned around the English.
Now there is one more test in Wigan before Luke can put up his feet for a few weeks. He has a family trip with his wife and children before he returns to Auckland to try and make some history with the Warriors.
Kiwi test records
55 Ruben Wiki 1994-2008
46 Stacey Jones 1995-2006
46 Gary Freeman 1986-1995
45 Stephen Kearney 1993-2004
41 Simon Mannering 2006-2015
38 Nigel Vagana 1998-2006
36 Issac Luke 2008-2015
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