Kolchak was originally two made-for-TV movies that aired in the early 70's, and featured the adventures of Carl Kolchak, a down-on-the heels reporter who ran afoul of a vampire in Las Vegas and an alchemist in Seattle. These movies proved popular enough that they were spun off into a series, which placed Kolchak in Chicago with the Independent News Service. Each week for 20 weeks he investigated various supernatural and supranatural creatures, ranging from aliens to vampires to Aztec sacrificial cults.
Although it only lasted one season on ABC, Kolchak has remained a cult favorite and been kept alive through the efforts of creator Jeffrey Grant Rice, Mark Dawidziak, and the folks at Moonstone Comics, who have two Kolchak comics going (see Links). There's an anthology of Kolchak stories coming out this year and discussion of a new Night Stalker (2005) series produced by The X-Files's Frank Spotnitz for ABC.