Millennium is a fictional organization from the manga series Hellsing by Kouta Hirano. The Millennium Organization is a Nazi group. Its name, "Millennium," is a reference to the "Thousand Year Reich" (with a millennium equaling a thousand years) which Adolf Hitler had wanted to establish in World War II. After the end of the war, this mysterious group pooled its resources and, with substantial help from the Vatican, relocated to Brazil and went into hiding. Millennium's researchers have discovered a way to transform people into vampires through unknown means (although it is hinted that some kind of surgery is involved), and monitors them using implanted computer chips.
Millennium seems to be a supernatural version of The Boys from Brazil. Most of the members are monsters of some sort, or have found a way to prolong their lives.