Balthromaw is depicted to be rather grumpy, and doesn't seem to be happy with his position as a pet dragon. However, he does become friendlier if meeting or bonded to rider that treats him like an equal or shares a similar point of view on the world.
Balthromaw is also sexual and promiscuous as he "soul-bonds" with many people. Although soul-bounding is limited to 1 person according to a dragon's contract, he doesn't feel bound to comply. He asks people for sexual favours when released onto Earth.
Balthromaw is summoned by a wizard residing in his realm and forced to be a servant to Morty. This displeases the dragon, but he begrudgingly accepts it and flies Morty through the air. After this, Balthromaw collects a large amount of gold and treasure, burying it underneath the Smith residence. When Morty asks Balthromaw what he wants to do, the dragon replies that he wishes to sleep until the end of mankind. Morty offers to split the difference and have it sleep for twenty minutes before flying again. Displeased by this, Balthromaw nonetheless agrees and disregards Morty's claim that they are having fun.
As it snores atop the mountain of loot, Balthromaw is woken up by Rick cursing at it; the dragon proceeds to incinerate him but is puzzled when Rick is not burned to a crisp. The dragon realizes too late that it was a decoy and the actual Rick gets the jump on it, outsmarting it. The dragon pledges his loyalty to Rick who begins to order it to leave but is amazed by the treasure Balthromaw has collected.
After hanging out throughout the day, the two disregard Morty's summoning and decide to enact a soul bond that binds Balthromaw and Rick's souls together. After both Morty and the Wizard witness this, the Wizard denounces Balthromaw as a slut dragon and whips him several times before taking him away. He later is sentenced to death by hanging, but Rick (along with Morty and Summer) manage to free him, fleeing into a nearby cave system. There, they meet up with several other slut dragons who mention the only way to undo the soul-bond is by killing the Wizard. The slut dragons and Smiths initiate a massive soul bond orgy and a phoenix dragon forms, enabling them to beat and kill the Wizard.
Balthromaw return to Rick and Morty's dimension with the Smiths; having started to see Morty in a different light, the dragon wishes to do a soul bond with him but Morty is disgusted by it. When he inquires if Rick would be interested in doing it, Morty disagrees and sends it away before closing the door; Balthromaw calls Morty a soul teaser before leaving.
Later in the post credits, Balthromaw is seen dragging his treasure on the street when a passing motorist stops and offers to pay him money for sex; the dragon angrily refuses saying he was done with humans and destroys the guy's car. After the motorist calls Balthromaw a slut and leaves, the Talking Cat approaches it. Balthromaw asks why it can talk, but does not pressure it further after hearing it is ashamed of the reason.
Balthromaw is a large dragon with various reddish brown markings all across its body. It has two prominent horns on each side of its head, yellow eyes and a beard.
- Balthromaw has a bunch of treasure and collectables like an original Ecto cooler juice box, Small Soldiers spin pops, and a Future self-titled album which was signed in the drugs Molly (aka MDMA, or Ecstasy) and Percocet (aka Oxycodone).
- Balthromaw's design fits the 'wyvern' type of dragons with two legs and two wings, as opposed to the four legged dragons from most fantasy works. It seems to be modeled after the design of Smaug in the 2010s The Hobbit film series.