There's a long-time theory that Bertrand is the lord of the Quadroads.
Back in 1.95: "One Year Later..." in about 811 PD, Grog found a very drunk stranger, one without any connections or people who would miss him, in the Quadroads district of Vasselheim and persuaded him to draw one card from the Deck of Many Things. The stranger was granted the ability to cast Wish twice and immediately used the first: "I wish that I was a powerful lord of the Quadroads." Thus, it was promptly done. He was dressed in finery and an attendant appeared at the end of the alleyway, asking the stranger how long he would be. The stranger admits he doesn't know the attendant's name, incorrectly says Grog's name back to him ("Grog Strongthings"), and then left with the attendant. Because Grog never got the stranger's name, he is known at the table and in the fandom simply as "the lord of the Quadroads". Matt remarked at the end of the scene: "There are many lords and ladies of the Quadroads, he's just now one of them."
Bertrand is introduced in The Search for Grog in the retinue of Holy Curator Uleas, representative of the Quadroads, suggesting Bertrand is from or otherwise associated with the area. He seems to generally have status, hence why he was at the meeting at the Platinum Sanctuary that Vox Machina crashed, but he has no apparent high-level connections in the city. Bertrand also has a hard time remembering people's names even if just told, evidenced in The Search for Grog / Bob and carried into Campaign 3.
On top of it all, Bertrand claims a lot of accomplishments, but he doesn't have anything to back it up; it's simply tall tales and boastful exaggerations, inflating his importance and knowledge in all manner of things. In the Search for Grog / Bob, he is a high-level character without having seemed to have done any adventuring, service, work, or study. These together build a sense that he's cheated his way to where he is, somehow.
Despite his participating in high-level combat, we somehow don't know his subclass; I wonder if he had one at all in the one shots, and I speculate that perhaps he did not, he's just a Fighter. I further add that, though we don't know much about him mechanically, Bertrand as introduced in Search for Grog / Bob is mechanically centered on the concept of luck, and of pushing one's luck: he has both the Lucky feat and carries a Gambler's Blade.
Bertrand being the lord of the Quadroads would neatly tie all this together: he is a very lucky man who pulled a phenomenal card out of a Deck of Many things on his first and only draw and instantly gained status that he didn't work for nor was brought up bearing, which created a massive gap in his background, his connections, and his ability that he has to somehow explain, which he attempts to do so by covering up with fanciful tales to paint him as justifiably here. Lucky and the Gambler's Blade is part of an ongoing tapestry of luck that includes that card; his mechanics spell a story about the coming and going of fortune. Maybe he didn't have a subclass to underscore what he skipped over getting to where he is, cheating and never gaining the skill. He is a simply a man of the Quadroads, a lord without connections because he isn't a lord at all, a charlatan and a teller of tall tales because he doesn't have another story to tell. A Wish, the first of two granted by drawing a card, gave everything to him in an instant.
As Bertrand says, in 3.01: The Draw of Destiny, "Not a noble, a knight is generous, but it was a title bestowed upon me, and I didn't shoo it away."
