Chloe Park immediately became popular during the sneak peek due to her being Adorkable and her cute appearance. It also helps that her voice actress also voices Ruby from Steven Universe.
Background character example: the Muslim girl wearing a hijab in the intro and at the college in "Chloe" has a few fans, despite presently lacking a name. One reason is that her design is considered one of the more unique ones out of all background characters since it's not common to see Muslim women in traditional garb in cartoons.
The Fireman that saved baby Grizzly in "Burrito". Some fanart has already popped up and some people have labeled him "The Most Wonderful Human Being Ever."
Lucy is quite well-liked as well due to being very friendly with the bears and being a very level-headed person. Despite this, it wasn't until the third season, where she made her second real appearance and became a recurring character.
Karla from "The Island", due to the maternal relationship she had with the bear cubs. Being played by Felicia Day helps.
Yuri from "Yuri and the Bear", for the same reasons as Karla, except only with baby Ice Bear. Being a Husky Russkie survivalist who made Ice Bear into who he is alongside his tragic past and paternal relationship with him certainly helps.
The three pregnant workout ladies from "Yard Sale", particularly on DeviantArt.
Another background character: the young man with brown hair and wears a red shirt, jeans, and sandals. He was one of the campers in "Primal", seen kicking Panda's chair in "Shush Ninjas", on the video on Panda's phone in "My Clique", and high-five'd Grizzly in "Tote Life". Nameless, he's referred to as "Sandal Guy".
