The Scion of Orcus was a necromancer. He was the final villain of one of Matt's campaigns. In the final battle, he was killed by the party, but killed Lady Sariel and raised her as a vampire.
The Red Gold
The Scion raised a necromantic tower and began collecting corpses to fuel his experiments. He gave red-colored gold to villagers in payment for the dead - the gold was enchanted and allowed him to detect when people died, so he could arrive and collect their corpses.
Behind the Scenes
Matt used the 4th edition adventure Keep on the Shadowfell as part of the inspiration for the final dungeon of the campaign. Originally the Scion's name was Kalarel the Vile, but Kalarel is the copyrighted name of the villain of that module and hasn't been reused in any of MCDM's products.
The conceit of buying corpses in order to build a tower to raise a dark power was borrowed from Shadows Linger, the second book of the Black Company series by Glen Cook, while the red gold was taken from The Belgariad by David Eddings.