In 2344, he was among the officers patrolling the Cardassian border that became acquainted with a young Chakotay. When Chakotay requested a sponsorship to get into Starfleet Academy, he told the captain that Kolopak approved, then kept Sulu as far away from Kolopak as he could so his lie wouldn't be found out. Chakotay admitted this to Kolopak when he informed his father of his intentions to leave the tribe and attend the Academy. (VOY: "Tattoo")
Background information Edit
This character was only mentioned in dialogue.
The Star Trek: Voyager Companion (p. 76), "It is assumed that the Captain Sulu who sponsored Chakotay at the Academy is either Hikaru Sulu who served under Captain Kirk on the Enterprise or Demora Sulu who served on the USS Enterprise NCC-1701-B." This reference, however, does not take into account the fact that Chakotay used the male pronoun "he" when referring to Captain Sulu.
As such, the Star Trek Encyclopedia (2nd ed., p. 70) suggested that this was probably intended to be a reference to Captain Hikaru Sulu, who would have been 107 in 2344. (Given Doctor McCoy's tour of the USS Enterprise-D as an admiral at age 137 (TNG: "Encounter at Farpoint"), this would not be as implausible as it might seem.)
The anthology, Tales from the Captain's Table, states that it was in fact Sulu's daughter Captain Demora Sulu who sponsored him (She would have been 76). The story also suggests an explanation for why Chakotay specifically referred to the Captain Sulu who sponsored him as "he" in "Tattoo".