Tempus is an agent of Immortus. He first appeared in "Giant-Size Fantastic Four" #2 (August, 1974). He claims to have existed in his own dimension since the "beginning of eternity", unchanging. The ennui of his existence has given a desire for his own death. Immortus claims to have created Tempus himself, fashioning him from "the very ether of Limbo".
Tempo has superhuman strength but this is not his key ability. His touch or blasts can rapidly age other beings. He needs to maintain contact for the effect to continue, loss of contact reverses the effect with the beings resuming their natural age and appearance. He can also cause other beings to relive painful memories, causing them anguish. Tempus can absorb force directed at him and redirect it at his opponent. His body can shatter on impact but the ether eventually restores it to its previous condition. He might be effectively immortal, rendering his quest for an end to his existence meaningless.
When first seen Tempus manipulated Willie Lumpkin into entering the time machine of the Fantastic Four. Willie was send on a directionless journey to various points in time, causing time paradoxes as he went. Tempus hoped that the paradoxes would cause an end to the universe. (According to "Marvel-Two-In-One" #50 (April, 1979), time travel and the paradoxes resulting from it cause the creation of alternate realities. The idea was set by John Byrne and has since been the rule for Marvel's time travel stories. The retconn would mean that Tempus' plan would actually cause the existence of new realities.)
The Fantastic Four (Human Torch, Medusa, Mr. Fantastic and the Thing) returned from space to find an Earth with vast differences than the one they had left. There were no cities in this Earth, only wilderness and the only humans were primitive hunters. Uatu the Watcher explained that history had been tampered with and sent the Four back in time to set things right. Reed and Johnny found themselves in the American Revolutionary War (1775–1783), having to rescue George Washington from British captivity. Willie had accidentally scared Washington's horse which threw the officer down. Washington had been unconscious when arrested. Ben and Medusa found themselves in 1928 Chicago having to rescue Willie from gangsters. Willie had been giving them stock market tips from the advantage point of four decades in their future. With both missions succesful, the Four and Willie were transported to Tempus' dimension. He proved quite a match for any of the Four until the Thing tripped him and the impact shattered him. The five time-travellers safely returned to the Earth of their own time.
In "Thor" vol. 1 #281-282 (March, April, 1979), Thor attempted to travel through time to investigate the history of the Celestials. He ended up in Immortus' Limbo where the Ruler of Limbo confiscated Mjolnir. Thor agreed to an alliance with the Space Phantom to get his hammer back. The two had to get past Tempus to reach Immortus. Tempus attacked the Asgardian with a club but Thor wrestled control of it. Thor proceeded in shattering Tempus' face.
In "Avengers West Coast" #62 (September, 1990), Immortus had taked control of the Scarlet Witch. The West Coast division of the Avengers (Hawkeye, Iron Man, Dr. Hank Pym, USAgent, Wasp, Wonder Man) and Quicksilver arrived t retrieve her but had to pass Tempus to do so. He picked Wonder Man as if he were a rag doll (according to Pym's description) and aged him to a very feeble old man. He then threw Simon to USAgent, knocking them both out. Pym's weapons, Hawkeye's blast arrows and Iron Man's repulsor rays could not hurt Tempus. But Quicksilver got the idea of hitting Tempus with Limbo's own materials, managing to hurt the giant. Tempus returned the favor by having them relive their most painful memories. For Quicksilver being hunted like a wild animal by European peasants, for Hawkeye his disillusionment when he learned his mentor Swordsman was a common thief, for Wonder Man "dying" because of the same ionic rays which had empowered him, for Pym looking down on the corpse of his first wife Maria when she was murdered, for Iron Man exploding shrapnel lodging within his chest area, for Wasp seeing her father Vernon Van Dyne killed by aliens, for USAgent seing his parents Caleb and Emily Walker shot down by assassins. The Avengers were all reduced to quivering helplessness.
Immortus contemplated if he should have Tempus kill the captives or not, reluctant to confirm his status as a villain. But meanwhile Agatha Harkness had entered Limbo unseen and managed to awake the Scarlet Witch from a catatonic state. Scarlet Witch knocked everyone aside, rescuing the seven fallen Avengers and confusing Immortus and Tempus. The Time Keepers then arrived to punish Immortus for acting against their command and actually threatening their own existence instead of protecting it. Tempus wisely did not intervene. (According to a later retconn these were not the Time Keepers at all but their counterparts and rivals the Time Twisters).
By "What If...?" vol. 2 #39 (July, 1992), Immortus had siphoned reality-altering nexus power from four realities and had evolved into a quantum wave. He set about recreating the multiverse. The Time Variance Authority opposed them and recruited four agents to go to Limbo and stop the process. They were Dr. Doom of Earth-772 (Earth Fantastic Five), Irondroid of Earth-90110 (Earth Ultra-Vision-Utopia), Thor of Earth-9260 (Earth-Thor:Thrall of Seth) and Wolverine of Earth-9250 (Earth Wolverine, Lord of Vampires defeated Punisher). They arrived in Limbo to find Tempus leading an army against them, composed of Dire Wraiths, Rama-Tut's robots and Space Phantoms. Tempus found he could not age either Thor (a god) or Wolverine (a vampire). The four agents were about to win when Immortus reset time back to the start of the battle, improving the strategy of his troops. The Dire Wraiths and the Space Phantoms respectively killed Doom and tIrondroid, leaving only Thor and Wolverine. However other agents of the Time Variance Authority had been sent to alter young Nathaniel Richards (the civilian identity of Kang and Immortus) preventing him from ever becoming a nexus being. With the conflict over Immortus became human again and Tempus continued serving him.
In "Avengers:Terminatrix Objective" #3-4 (November-December, 1993), Kang , a younger counterpart of Immortus, drained the life forces of the Council of Cross-Time Kangs (an organization including thousands of Kang counterparts and their successors from various realities) and used the energy to empower Tempus who grew to enormous proportions. Kang then send him against Alioth, an extra-temporal entity with ambitions of taking over spacetime. Alioth tried using his temporal energies to defend himself. Tempus simply fed on them and kept on growing. The two opponents were locked in a stalemate which according to Kang's plans would last forever.
in "Avengers Forever" #1 (December, 1998), Immortus summoned Tempus, back to normal size and power levels, to use against Rick Jones. Tempus started draining lifeforce out of Jones but Kang arrived and shashed Tempus to pieces. Kang and Immortus were locked in conflict at the time and Jones was an ally of Kang. In #3 (February, 1999), Tempus was briefly seen by Immortus during his confrontation with Kang. In #7 (June, 1999), Tempus faced Goliath/Clinton Francis Barton who shattered him to pieces. His revival has not been depicted.