Shortly after Ash Williams had left 1300 AD, the Kandarian Demon was unleashed once again after Ash misspoke the words when trying to return to his own time. The demon had managed to possess Lord Arthur, Henry The Red, and Sheila, leaving The Wise Man as the only person left to seek Ash's help in the 21st Century.
After returning with Ash to The Cabin where everything started to retrieve the Necronomicon Ex-Mortis, the Wise Man and Ash traveled to Egypt, specifically to the temple where the book was created in order to destroy the Book of The Dead. While standing outside the temple, The Wise Man was stabbed in the by Ash's Evil Hand (who had hid away in a backpack while the two were at The Cabin). Ash buried The Wise Man just outside the temple, marking it with a large wooden cross made from sticks. Ash later completed the mission for The Wise Man and manages to re-write history, saving The Wise Man from his untimely death.
As A Deadite
After aiding Sheila in her quest to return to Ash in the 21st Century, Sheila's evil Mirror Dimension counterpart took over Castle Kandar and turned Lord Arthur, Duke Henry, and The Wise Man into Deadites. The four of them took "the slow path" to the 21st Century, and founded the Weenieville fast food restaurant chain sometime in the late 20th Century. When Ash Williams and his new assistant Sugarbaby investigated Deadite activity from one Detroit Weenieville store, the soul of the "good" Ash was sent out of his body and replaced with the spirit of Evil Ash. During Evil Ash's rule over Earth, The Deadite Wise Man was one of Evil Ash's most trusted henchmen, and was sent on a mission to kill the original Ash after it was discovered that he had returned from "the afterlife". Ash killed the Deadite Wise Man and later re-wrote time, causing these events to never occur.
Unwilling Ruler of Castle Kandar
When Ash and Sheila returned to 1300 AD, the two discovered that Lord Arthur and Henry The Red died in battle, fighting what was left of Evil Ash's original army. After their passing, The Wise Man took it upon himself to help the peasants and soldiers that hadn't died and led them to safety. The Wise Man then informed Ash that before their death, both Lord Arthur and Henry The Red chose Ash to be next in line for their respective thrones. After Ash accepted the title of King, The Wise Man told Ash that if Sheila was to marry Ash and live together in 1300 AD, she would die by the hands of the Deadites. Ash then returned to the 21st Century by himself, leaving Sheila in the care of The Wise Man and her newly resurrected brother.
Move To The 21st Century
Once again returning to the 21st Century to inform Ash of a danger in the past, The Wise Man decided that he was going to stay with Ash in the future since he couldn't keep going from 1300 AD to the future to warn Ash of threats without disrupting the timestream. There he remained with Ash, even helping him set up a Deadite-Hunter-For-Hire business online.
Since the Wise Man wasn't present for Evil Ash's second attempt at world domination, it's safe to presume that at some point after Ash teamed-up with Cassie Hack, the Wise Man passed away or was killed in battle.
- While living with Ash in the 21st Century, the Wise Man went by the name "Merlin" (or "Merl", as Ash called him). It is unknown if this was his real name or if it was just an alias.