"He had a presence about him," remembered Kearney.
"He was wonderful company and great to have around but he was pretty cheeky and a bit of a ratbag. As my grandmother used to say, he was a bloody humbug."
Even back then, it was obvious he could play. Luke didn't look out of place on debut in the Centenary test at the Sydney Cricket Ground and he performed well in a struggling Rabbitohs team.
Souths didn't fire in 2008 - they finished third from bottom - but Luke did.
He averaged more than 80 running metres and almost 20 tackles per game, and crossed for six tries.
"He stood out from an early age," said Kearney. "He could do it all and was even kicking goals.
"He had some real talent but it was the polishing up of the rough edges that needed to happen over time."
Luke was a bit of a loose cannon. League is a tough sport, played on the edges, but he sometimes took it took far. There was the clash with David Shillington that started a brawl at Eden Park in 2010 and a cannonball tackle on the same player in the 2011 Four Nations. Then there was the awful incident with Rangi Chase in the same tournament, when he admitted trying to break his cousin's leg.
"I just saw red," he said at the time. "When you come up against your family, you want to outplay them. I didn't outplay him. I tried to break his leg. It was the wrong thing to do."
New Rabbitohs coach Michael Maguire was watching, unimpressed. In a heated phone call before the start of the 2012 season, he promised Luke "we are going to change you".
That Chase incident was the nadir. There were other incidents - he was dropped for breaking team curfew when he attended a friend's stag party, and later that year for a bust-up with team-mate Scott Gedddes at Souths training - but was growing up.
"[That change] probably came after the Rangi Chase incident," he told the Herald in 2013. "It didn't just affect me. It affected everyone around me. I saw it as a wake-up call, a kick up the arse. Ever since then I have been on a happy road ... happy with how I am going."
"It's been a process for him but over the last three years he has taken it to another level," said Kearney.
"He has really developed as a leader, not only at club level but also in the Kiwi environment. He has really come on."
Issac Luke
NRL debut: 2007 (round 12)
NRL games: 188
Kiwis debut: May 9, 2008
Kiwis tests: 33