Anton Arcane is ST's oldest and greatest foe. He first appeared in issue #2 (1972) of the first SWAMP THING series.
From his castle in the Balkan Mountains, he experimented with the creation of artificial bodies, resulting in the nightmarish Un-Men. The elderly Arcane hoped to find a means of indefinitely prolonging his own life.
In issue #3 (1973) of the first series, Anton's brother Gregori Arcane, Abby's father, was blown up by a leftover WWII landmine. Anton rebuilt him as the Patchwork Man, a Frankenstein-type assemblage of body parts.
Arcane appeared to be killed on several occasions, but was re-built by his Un-Men. Before Alan Moore took over as writer, Arcane had settled into a monstrous half-insect, half-robot body.
According to the 1994 Vertigo limited series AMERICAN FREAK: A TALE OF THE UNMEN (by Dave Louapre & Vince Locke), Arcane's Un-Men were siezed by the government, but had offspring. In 2007, an UNMEN series ran in DC comics' Vertigo line. Newsarama has the story.
Arcane's first name was never revealed until the 1982 movie based on the SWAMP THING comic book. The handsome villain in the film was named Anton Arcane, and beginning with DC's WHO'S WHO (issue #1, March, 1985) the comic book Arcane was named Anton.
Notable appearances in SWAMP THING:
SAGA OF THE SWAMP THING #27 "By Demons Driven"
Although it is not directly stated that it is Arcane, he appears to Matt Cable in the form of a fly, and takes posession of his body in an effort to return from the dead, unbeknownst to Matt's wife, Abby.
#29-31 and Annual #2
In possession of Matt Cable's body, Arcane tortures and kills Abby and sends her to hell. Matt summons up the willpower to break free of Arcane at the cost of his own life. ST manages to save Abby. Arcane remains in hell.
As a torture while in hell, Arcane is given a glimpse of his brother Gregori's (the Patchwork Man) anguished reunion with Abby, but Arcane enjoys it.
#82 and #83
"Brothers in Arms"
During his backwards journey through time, ST encounters Arcane in the 1940's. Arcane, manipulating Adolf Hitler, has incited World War II as an opportunity to collect bodies to experiment on.
Later (or earlier, actually) during World War I, ST finds himself in the body of Albert Höllorer, an earlier swamp elemental. Through painful dissections of ST's body, Arcane discovers anatomical knowledge that will eventually enable him to create the Un-men. Abby's grandmother helps ST escape.