You may think you know what Throg is about just by looking at him (especially after Loki Season 1’s fifth episode), but I promise there’s more to it than that. Throg actually used to be a man named Simon Walterson, who pissed off a witch after he couldn’t pay a tab after speaking to his dead wife in the afterlife. He was transformed into a frog and, in a strange twist of events, came across Thor, who had also been turned into a frog. Long story short, Throg wielded a sliver of Mjolnir and gained the power of Thor in his frog form.
Article source: https://www.cinemablend.com/news/2570678/following-howard-the-duck-6-offbeat-marvel-characters-mcu-introduce-werewolf-night-man-thing