He is a weightlifter, since he has competed in the Anchor Toss Competition in the episode "MuscleBob BuffPants." He is seen to be rather muscular, possibly from his exercise routine. He hangs out at the bar usually just to listen about people's workout routines, as evidenced in "MuscleBob BuffPants."
He is a muscular orca and has a black backside with dark gray arms and legs, and he has a dark white underside. He wears light blue shorts that resemble swim trunks.
Don can be seen with the rest of the people dancing on the beach when SpongeBob comes with Bubble Buddy. SpongeBob proceeds to say "Shake it! Shake that bubble butt." The fellow dancers think SpongeBob is addressing it towards them, causing them to leave the beach.
Don is one of the customer that buy SpongeBob and Patrick's ink lemonade.
In one episode, someone says that Sandy is the only mammal in Bikini Bottom, but Pearl, Craig Mammalton and Don the Whale are also mammals. What that someone may possibly be referring to is that Sandy is the only land mammal.