Taj Gibson told The Post in August his chief job as a new Knick was to mentor center Mitchell Robinson. But the 34-year-old defensive bruiser hasn’t forgotten about the Knicks’ other big man, former Bulls teammate Bobby Portis.

Portis, 24, cited Gibson as one of his first mentors when they were together in Chicago his rookie year. The Knicks thought enough of Portis to lavish a two-year, $31 million deal (the second is a team option) on him.

“I had great veterans in front of me that really showed me the ropes,’’ Portis said of his Chicago days. “I think without those guys I wouldn’t know how to do things the correct way.’’

Gibson is impressed with Portis’ development.

“He’s just the kind of pro we thought he’d turn into,’’ Gibson said. “We were real tough on him. He was able to learn behind a lot of tough veterans. You could see it paid off the way he handled it on and off the court. It’s good to see Bobby mature into a solid player.’’

During free-agent recruitment, Portis was told Robinson likely would be starting center. Portis told The Post during the summer he’d shoot for Sixth Man of the Year. But everything is fluid.

Coach David Fizdale said he has been impressed by Portis’ communication on defense. There’s some thought Robinson could be better coming off the bench to avoid the foul trouble that plagued him when he started games last season as a rookie.

Portis is known for his offense, improving his 3-point shot (39.3 percent in 2018-19). But Fizdale likes what he sees on defense.

“He’s a warrior,’’ Fizdale said. “He really takes the challenge when it comes to defending individually and really is a good communicator and gets guys where they’re supposed to be.”

Robinson was a startling surprise as a rookie project last season. Whether the shot-blocking phenom grows dramatically in his sophomore year is the season’s most compelling mystery. Gibson says that is one of his jobs.

“That’s my guy,’’ Gibson said. “He has a lot more to offer than what you see. He’s only scratched the surface.

Gibson was thrilled to meet at camp Knicks legend Bernard King, who grew up in the same Fort Greene projects as Gibson. They both attended P.S. 67. Gibson wears jersey “67’’ as tribute.

“We tried to build off of what he and his brother [Albert] left behind,’’ Gibson said. “Sixty-seven is a strong number in my neighborhood.’’