Dreambooth is what I'm using now, but I think I remember the concept had a specific name, something like 'context transfer' or so (pretty sure that was not the term) and tools that were pretty good at it that came out before Dreambooth. If I could at least remember the term it might be easier to search for them.

Dreambooth is ok at it, but it requires multiple images (you often read 30, but I've actually had decent results with as few as five) to recognize what it's supposed to replicate. I remember there were tools that were more adapted to the workflow "create a humanoid cartoon character with a bunny face", pick one image that you like, and then "now show that same character in scene X, eg teaching in a classroom" or "wearing a cowboy outfit".