Tantrum is a Decepticon or Predacon from the Aligned continuity family.

"Look, we should at least pretend the Aligned continuity fits together—"
"Screw up, Starscream, they can suck on my two conflicting backstories!"

Tantrum is a Decepticon/Predacon bull. His exact origins and species vary by universe. Whatever the case may be, he sure doesn't like that Starscream guy for one reason or another.

Fiction

Aligned novels

During the exile from Cybertron of the Autobots aboard the Ark and the Decepticons aboard the Nemesis, the two ships had happened upon the planet Aquatron, on which many of the Autobots and Decepticon had been captured and taken into custody by the planet's Sharkticon inhabitants and their masters the Quintessons. The Decepticon Starscream had managed to escape back to the Nemesis, leaving behind the planet-bound Decepticons led by Megatron. As Starscream appeared to be avoiding rescuing the Decepticon leader, Tantrum, Headstrong, Rampage, and a number of other Decepticons entered the bridge to confront Starscream in protest of his apathy, quickly changing the Seeker's mind. Tantrum, along with the others, cheered in the excitement of rescuing their glorious leader. Retribution

Titan Prime comic

He's angry that he wasn't in the show.

Fed up with Megatron having the mighty Predaking, Starscream decided to create his own Predacon beast. 'Borrowing' Shockwave's lab, he cloned a new Transformer from fossil remains and his own CNA.

Starscream then expected this new lifeform to do what it was told. When the beast wouldn't listen to him, Starscream struck him. The beast grew furious, transformed to bull mode, and chased Starscream around the ship with intent to kill! (That's how he was named Tantrum!) Vehicons and Insecticons were ripped to pieces when they got in his way but the violence did serve to calm Tantrum down.

Back in robot mode, Tantrum announced he was a superior Transformer to everyone on board and he planned to kill the inferior Starscream. The Decepticon tried to talk him down, advocating for a more subtle way to conquest. Tantrum dismissed that, stating he was learning from Starscream's mistake and would show him how to take power!

So Starscream blew him up with a direct missile strike.

He later picked up Tantrum's remains and thought about having another crack at creating a Predacon... Starscream's Beast

Notes

• Comic Tantrum is a rarity in being a Predacon whose beast mode isn't based on a draconian, reptilian, or mythological creature, but instead a bovine.