episodes also deal with the relationship between Mulder and Scully, originally platonic, but that later develops romantically. Mulder and Scully are joined by John Doggett (Robert Patrick) and Monica Reyes (Annabeth Gish) late in the series, after Mulder is abducted. Doggett replaces him as Scully's partner and helps her search for him, later involving Reyes, of whom Doggett had professional knowledge. The initial run of The X-Files ends when Mulder is secretly subjected to a military tribunal for breaking into a top secret military facility and viewing plans for alien invasion and colonization of Earth. He is found guilty and sentenced to death but escapes punishment with the help of the other agents, and he and Scully become fugitives. Mythology As the show progressed, key episodes, called parts of the "Mytharc", were recognized as the "mythology" of the series canon; these episodes carried the extraterrestrial/conspiracy storyline that evolved throughout the series. "Monster of the week"—often abbreviated as "MOTW" or "MoW"—came to denote the remainder of The X-Files episodes. These episodes, forming the majority of the series, dealt with paranormal phenomena, including: cryptids, mutants, science fiction technology, horror monsters, and religious phenomena. Some of the Monster-of-the-Week episodes even featured satiric elements and comedic story lines. The main story arc involves the agents' efforts to uncover a government conspiracy that covers up the existence of extraterrestrials and their sinister collaboration with said government. Mysterious men constituting a shadow element within the U.S. government, known as "The Syndicate", are the major villains in the series; late in the series it is revealed that The Syndicate acts as the only liaison between mankind and a group of extraterrestrials that intends to destroy the human species. They are usually represented by Cigarette Smoking Man (William B. Davis), a ruthless killer, masterful politician, negotiator, failed novelist, and the series' principal antagonist. As the series goes along, Mulder and Scully learn about evidence of the alien invasion piece by piece. It is revealed that the extraterrestrials plan on using a sentient virus, known as the black oil (also known as "Purity"), to infect mankind and turn the population of the world into a slave race. The Syndicate—having made a deal to be spared by the aliens—have been working to develop an alien-human hybrid that will be able to withstand the effects of the black oil. The group has also been secretly working on a vaccine to overcome