Where to begin with Magus...originally he was from the year 12,000BC and originally named Janus (Schala's little brother). When his mother, Queen Zeal, summoned Lavos the first time, Janus was sucked into a time portal (or "gate") and ended up in the year 600AD where he was found by Ozzie and re-named Magus.

Magus was in the process of summoning Lavos to the year 600AD when Crono and company interrupted him. Magus was planning on defeating Lavos in order to extract revenge for ruining his childhood.

After the battle with Crono and company, Magus was sucked into the "gate" as well. Though he didn't end up in 65,000,000BC, instead he was sent home to 12,000BC.

Nothing is known about what went on with him prior to Crono and company appearing in 12,000BC because we were following their actions in 65,000,000BC. And the events that led up to him joining the group are too many to list. But know this - Crono dies protecting everyone from Lavos. Schala sends the survivors to the earthbound village and the Kingdom of Zeal falls and is never heard of again.

Though it isn't until after the destruction of the Blackbird, a powerful airship that Belthasar built, does Magus join the group. Even then it is optional - you can either fight him or have him join you. If you fight & defeat him Frog changes back to a human. If you have him join you, he's a powerful ally...

As far as magic is concerned, Magus is ^the^ most powerful of all the characters, well except for Spekkio. Here's a list of all the magic attacks that Magus can do, though his main type of "Tech" is Shadow, he can preform other spells as well.