Major Story Arc
Vili with his 2 brothers Odin and Ve, were part of the first few Asgardians who warred with the Frost Giants, They helped build Asgard also. The 3 brothers learnt that Surtur was plotting to destroy the nine worlds with his giant flame sword and ignite the Eternal Flame of Destruction; this would have led to Asgards destruction. So the 3 brothers set out to defeat him and avert destruction. They could not fight him individually, so the 3 merged into a giant that was the size of Surtur and they succeeded in shattering his sword, meaning he could not go through with his plan, they then returned to their individual forms and took the Eternal Flame of Destruction and fled.
Powers and Abilities
Vili was never shown to have a certain amount of strength, but it was indicated he was 1/3 of the strength of Odin, this was the case because once he died, Odin got some of his power and in turn this led to the Odin force being created. Vili can probably lift between 30-35 tons, this was just higher than the average Asgardian.
He has never actually been shown to posses many powers. But he has the standard Asgardian power-set regardless, Super-strength and speed. 3x more durable than a human. He could probably have some magical ability because of his power that was transferred to Odin.