Wiseman was once a human with godlike abilities called the Mad Dictator Phantom from the 23rd Century. In a fight with Neo-Queen Serenity, ruler of Crystal Tokyo and the Silver Millennium, she banished him to the tenth planet of the Solar System, Nemesis, where he remained for several centuries. He eventually bonded with the planet's core and became the Death Phantom. Taking on the form of the cloaked Wiseman in the 30th Century, he enticed a group of rebels from Earth to come to Nemesis, and there they became the Black Moon Clan. Powered by the Evil Black Crystal at the planet's core, the Clan were convinced that the Queen's ability to keep everyone on Earth young and immortal by using the Silver Imperium Crystal was a blasphemy onto God. One day, the Clan launched an attack on Crystal Tokyo which turned the city into a wasteland and caused the Queen to go into a deep sleep after she'd been attacked.
The Clan chased after her daughter, Chibiusa, to the 20th Century, while trying to find the Silver Imperium Crystal. One after another, the Clan's subordinates were killed by Sailor Moon, Serenity's younger self, but they managed to abduct three of the Sailor Senshi and brought them to the future. Following after them, Wiseman's true form slowly started to reveal itself when he brainwashed Chibiusa and turned her into Black Lady. He then forcibly brainwashed his only two pawns left, Prince Demand and his brother Blue Saphir, when they refused to go along with his plans. Demand tricked Wiseman by revealing that he used the abilities he bestowed on all members of the Clan to avoid being brainwashed. Being forced to kill his borther, Demand tried to kill Wiseman, but discovered that there was only a skeleton undernath the cloak. Wiseman revealed his true form as both the Death Phantom and Nemesis to the Sailor Senshi and Demand as he tried to destroy the Tokyo of the 20th Century. When Demand was killed by Sailor Moon and Tuxedo Mask, the Death Phantom lost his advantage when Chibiusa broke free of her brainwashing when her only friend, Sailor Pluto, was killed in the battle. Becoming Sailor Chibi Moon, mother and daughter finally destroyed him in a double attack.
The ironic thing about Wiseman's plan is, that if he were to destroy the Tokyo of the past, he would've prevented his birth.