Cyclonus was a creation of Unicron.
U.S. Animated, Japan
After the defeat of Unicron, Cyclonus spent months relentlessly searching for Galvatron and finally found him on the planet Thrull. Cyclonus remained loyal to Galvatron even though the latter went insane from the lava bath on Thrull. However, he was not blindly loyal. He would always guide Galvatron and stand up to him for his own good. He became the inspiration for the other Decepticons to go on, and even once tried to help cure Galvatron of his insanity by taking him to the planet Torqulon. He freed Galvatron when it became apparent that Galvatron was going to be destroyed, and Galvatron emerged a better leader. Cyclonus has a strong sense of honor, and believes warriors should die in battle. He even saved the life of Ultra Magnus because this belief.
Cyclonus continued to act as Galvatron's lieutenant but was seemingly later replaced by Sixshot as Galvatron's most trusted warrior. Cyclonus and Scourge were not seen after Galvatron's death, though there was no sign that they left the Destrons.
Marvel U.S., Marvel U.K.
In an alternate future, after Unicron destroyed Cybertron, the Decepticons conquered the North American continent of Earth. Cyclonus was bored at waiting for the humans to strike at them so Galvatron could absorb the energy from the nuclear missiles. He and Scourge were attacked by Autobots, and the latter perished in the struggle. Disgusted that Cyclonus was bested by an Autobot, Galvatron saved Cyclonus so he could destroy him personally.
Cyclonus first appeared with Galvatron and Scourge in the year 1986 after time traveling to build a gigantic cannon to destroy Unicron. They left after being tricked into believing history could not be changed.
In the aftermath of the battle with Unicron, Galvatron was missing, and Death's Head attacked Cyclonus and Scourge and interrogated them on Galvatron's whereabouts. Cyclonus and Scourge later helped Death's Head kill Shockwave and acted as co-leaders of the Decepticons until they were sent back in time. In the 20th century, they fell under the command of Scorponok and aided him in attacking Nebulos, becoming Targetmasters.
Cyclonus and Scourge later joined the 20th-century Shockwave. However, they tried to track down Galvatron to steal his time-jump device and return to the future to rule the Decepticons, and failed to do so. Shockwave soon learned of his future death at the hands of Cyclonus and Scourge and ordered the clone Megatron (whom he revived and was planning to set against Galvatron) to kill them. Megatron managed to destroy Cyclonus by beheading him.
However, upon Cyclonus's death, a time storm grew in the future that could only be ended if the time-travellers returned to their time. Scourge flew into it, Galvatron was ripped apart by it, and the time storm ended when Shockwave fired Cyclonus's body into it.