(This lore is a hybrid of the old Summoner lore, and the new retconed lore.)
For decades, the Institute of War controlled and restricted the interactions between the City Scapes. At the height of it's power, the institute made a critical mistake, and attempted to restrict summoning magic from non-Institute approved mages. In the coming weeks both Noxus and Demacia would begin training thousands of their mages in Conjuring as protest.
With Champions from both factions refusing to "Keep the peace" other smaller city states began doing the same. After this victory, the smaller city states began demanding more and more freedoms, that led to more conflicts between the Summoners and their Champions.
Eventually very few summoners remained at the institute. The majority of them had returned to their own City States. Only the most loyal and most invested summoners remained to contain what power they had accumulated, such as control over the nexuses, and monsters like Nocturne and Fiddlesticks.
Nearly a decade after the protests, Noxian and Demacian Troops camped on either side of the Institute. Terrigon, a summoner of great moderate importance exited the Gates of the Institute to speak with the Noxian Army's Leadership. Sion and Darius stood at the front lines glaring.
"Who among you leads this..." Terrigon started.
"I do!" Darius Interrupted, "Now surrender the gates Summoner. Noxus claims this territory, as well as everything and everyone on it."
"The Institute will not surrender to your threats. We were peace keepers, we can be that again."
"You are Terrigon aren't you? You hail from Zaun. Return there. Leave this place to us." Darius stepped closer to the threshold dividing Institute land and Noxian land.
"Do not take that step if you wish to survive this encounter," Terrigon warned, "I have come to speak to you as a cutesy to prevent Noxian casualties."
"What will happen if I take this step?" Darius lifted his foot.
"You will die."
"If I take this step, what will kill me?"
Terrigon weighed his options. Noxians would be able to spot his lies, and there truly were no more magical barriers protecting the Institute after Zilean returned to Shurima. "I will."
Terrigon crawled into a ditch just outside the Noxian Prison. He was free, for the most part. The shackles keeping his wrists together were restricting his magic. They thought they could contain all of his power, but they had been mistaken.
He continued on his elbows and knees like this until he felt that the watch towers would not be able to spot him. It would not be long before they discovered he was missing, and he would have to get far away, if he was ever to reestablish the Institute of War.
Terrigon works best in the mid lane, functioning mid range mage. He needs to use his mobility to dodge enemy attacks, and get close enough to farm and regain stacks of freedom. Mid to late game he can close in using multiple flashes and kill targets with a Q-E2-AA-W-E1 combo. He deals the majority of his damage at close range, though he can lay down minor damage from afar when no creep are present, or major damage if he has vision of a recalling enemy.
He can be shut down by enemies zoning him from minion waves, but can roll over enemies that allow him to farm and close in.