Book of Shadows

TEMPUS

Season One

Tempus was sent by the Source in 1999 to help the demon known as "Rodriguez", to defeat the Charmed Ones. So every time Rodriguez failed to kill them and got vanquished, Tempus reset time, allowing Rodriguez to learn from his mistakes and get another chance. Tempus and Rodriguez were the only ones who knew about this, until Phoebe began to feel that they are in a time loop, which she theorized may have been because of her power of premonition. But later Prue and Piper began to realize it too, repeating the same day over and over again. Rodriguez killed Andy Trudeau, and once the sisters figured out what had been happening, they cast a spell to accelerate time, therefore breaking the time loop and taking Tempus out of his time. Tempus, defeated by the Charmed Ones, fled back to the Underworld and Rodriguez was vanquished by Prue.

Season Three

In 2001, the Charmed Ones and the demonic world were exposed on live television. The sisters figured they needed to contact Tempus to reset time to before they were exposed, but none of them knew how. Their Whitelighter, Leo Wyatt decided to go to the Underworld, and asked Cole Turner to contact Tempus. Cole said he did not have that kind of power. Phoebe suggested for him to go to The Source Of All Evil, ruler of the Underworld, and ask him to contact Tempus to reset time, as exposure is also a problem for evil. Once Cole asked The Source, The Source stated that Tempus was still weakened from his last encounter with The Charmed Ones, and doing so again could destroy him. But later The Source accepts their offer, after making a deal with Phoebe for her to stay in the Underworld, and used Tempus to reset time. ("All Hell Breaks Loose")

Although not implicitly stated, it is implied this is what killed him. Also, Tempus does not actually appear in this episode, he is only mentioned. Meaning he was not actually killed by the Charmed Ones which most are when coming into contact with them

In 2006, the demon Tam asks a Possessor Demon, who she is trying to bring back from the dead. Tam guesses, and asks if it is Tempus, Barbas, Zankou or the Seer. The Possessor Demon later revealed and successfully brought back The Source