Boris and his wife and two cubs were living okay back in Siberia, but this was ruined when humans moved in. After the tundra was littered in garbage and food became scarce, Boris found hope in the form of a poster of Australia, and decided to turn themselves into a circus in order to get there, though his own parents refused to join them, much to Boris's sadness. They eventually arrive in Australia and Boris left to scout around for a new home.
He first (and only) appears in this very episode. Shifty Dingo tackles him by mistake after playing some game that involves wearing a blindfold and catching others, and when Shifty sees him he freaks out. Luckily Boris turned out to be friendly as demonstrated when he cuddles and kisses Blinky. It took a while for the Blinky Bill Gang to discover that he is a polar bear (and a Russian one at that, as proven by Boris's accent) since they've never seen his kind before. Boris then explains how he got to Australia in the first place: because the humans were polluting their home and Boris and his family decided to move out. He hoped to find a new home in Australia and the main characters agree to help. It wasn't all that successful; a wombat's tunnel was too narrow for him and a pond was too warm and shallow for him. He eventually gave up and went back to the circus, bringing Blinky and co with him. Upon sneaking into the circus-tent a pair of clowns catch them but never intended to chase them, though they do eventually chase Blinky for a bit. Blinky is then introduced to Boris's wife and cubs, then they receive a letter from Boris's parents saying that a nature-preserve had been established; meaning that Boris and his family could go back to Siberia. Boris encouraged Blinky to accompany them but he refused, though Boris was okay with it and instead the bears decided to give him their Russian tea jug for when he and his friends got back to Green Patch, promising to meet again someday.
Boris is quite nice despite his height, which can sometimes get creepy as upon meeting Blinky he picks the koala up for a hug and smooches Blinky on the cheek.