We've already touched on how Kathryn Janeway, and by proxy her actress Kate Mulgrew, appeared in over 200 episodes across Star Trek. For 30 years, and across two series, Mulgrew has built up a huge resume in Star Trek alone. She surpasses all of her Voyager and Prodigy castmates in appearances, and only bows out to three people; Colm Meaney, Michael Dorn, and Majel Barrett.
When we look at her fellow Voyager castmates, she nearly doubles some of her colleagues, like Jeri Ryan. The actress, who played Seven of Nine across two series (Voyager and Picard), has appeared in 125 episodes. 100 of them just with Voyager. While that's an impressive number, more than anyone on Star Trek: Enterprise ever got, it's actually not that impressive against her Voyager colleagues.
Every core cast member of Voyager, save for Ryan and Jennifer Lien (Kes), has been credited for 168 episodes. Ryan was credited with 100 (101 via IMDB), while Lien was credited with 70. Despite that, one of the crew members who wasn't a series star has more appearances than both Ryan and Kes and no, it's not Majel Barrett.
While Barrett has 110 credits on Voyager (via IMDB) all of which as the ship's computer voice. Even she isn't the person in question. No, the one person who appeared the most on Voyager who wasn't a series star is a man named Tarik Ergin. He's not a name you likely know, and his character, Ayala, is someone you probably can't pinpoint.
Yet, according to IMDB and Star Trek's wiki, Memory Alpha, Ergin is credited for at least 123 episodes (Memory Alpha) and at most 126 (IMDB). So who is the character he played, Ayala? Well, he was a former member of the Maquis, who would be given the rank of Lieutenant Junior Grade upon the merging of crews.
Ayala as a member of the Val Jean, which Chakotay was the captain of ended up being the third most featured Maquis member. When the Val Jean was destroyed after it was pulled into the Delta Quadrant, Chakotay, Ayala and the rest of the Maquis settled in onboard Voyager. He'd serve many functions for Voyager, working everywhere from engineering and operations, to eventually security.
While a minor character on screen, Ayala would actually serve a major role for Voyager, often taking over the bridge when the more senior members of the crew were called away. Despite being a member of the Maquis, with very little background given to him, we do know that he stayed with Starfleet upon his return to the Alpha Quadrant.
In Star Trek: Picard, he was listed as a member of the USS Dauntless and served as a flight controller for the ship, though he wasn't seen in the series itself.
As for the man who brought him to life, Ergin didn't stop acting for Star Trek after Voyager ended. He'd go on to appear in eight more episodes of Star Trek: Enterprise. However, he wasn't officially credited for any of those episodes.