Professor Len Lewis was an archaeologist who believed that the mythical Tree of Life (Yggdrasil) was not just a Norse myth but was in fact real. After extensive studies, Len tracked its location to a swamp in Africa. However before he could release his findings, his assistant shot and killed him, and took a sample of Yggdrasil's branches (which he planned to sell to the highest bidder).
However, energy flowed from the legendary tree into Len and brought him back to life. Yggdrasil had infused Len with its raw elemental powers and made him "a Lantern to light the darkness". Now calling himself the Green Lantern, Len was a living being of green energy and linked to the forces of nature. Using his elemental powers he fought monsters and the cult formed by the evil Reverend Dominic Darrk. Later he gathered the world's greatest heroes to form the Justice League for his reality.
For more information see: Convergence
Len Lewis and the rest of The Justice League of Earth-6 are killed and destroyed by Telos and his army.
Green Lantern Season 1
Green Lantern Season 2
In The Multiversity Guidebook Len Lewis and his Earth are given the designation of Earth-6.
As Green Lantern, Len uses the energy of the tree Yggdrasil to manipulate the forces of nature. His green energy can be used to create whirlwinds, ignite fires, cause earthquakes, generate tidal waves, and influence plants and animals. He can focus his green energy into explosive blasts, or channel it into others to heal them. Green Lantern can also fly at high speeds. When Len uses his powers, his skin glows green and the rune of Yggdrasil (which looks like a lantern) burns brightly on his chest.