This would probably be Kagark, a half-orc fighter/rogue I created as a throwaway character during the caravan portion of Horde of the Dragon Queen. I played him as sort of a dim Cookie Monster type, and had him flirt with a player’s barbarian (because of course he’d be attracted to a bruiser of a woman) just as a way to sort of bring the player out of her shell.
He ended up staying with them through the end of the adventure and I had several requests that he make the transition with the survivors into my follow-up Spelljammer campaign. By the end of that campaign, he and the barbarian, Veya, were officially a couple.
Not bad for a character I had talk like Cookie Monster because it was easy (and funny) and I only intended to be a background NPCs.