Just made a realisation about the Trip Trap. Here’s the Book of Fables entry concerning it:
The oldest bar in New York City, the Trip Trap was established in 1725 in secret by Starkad - the legendary Viking and reprobate - as a place for Fables to meet and drink and commiserate. Known then as the Grammarian’s Tavern, he eventually lost it in a bet to a tribe of mountain trolls, who quickly renamed it and made it their own. Holly is the current proprietor, having inherited it from her mother when she died in a boating accident in the early 20th century.
Starkard was, indeed a Norse Fable, even mentioned in Beowulf. Given how few Norse Fables are mentioned to have got out of the Homelands, I do have to wonder if Gren was already a regular at the bar when Starkard ran it. When Holly’s family took it over, they just inherited this surly regular, too, who refused to leave.
Then they grew on him and he just watched over them forever.