Showtime and corporate parent CBS (NASDAQ:VIAC) have some bloody shoes to fill with ratings winner Dexter, which recently entered its eighth and final season. The cast and producers said goodbye to fans last week at San Diego Comic-Con.

Michael C. Hall as serial killer Dexter Morgan. Source: ET Online, Showtime.

Dexter stars actor Michael C. Hall as a Miami crime-scene analyst who doubles as a serial killer of crooks. The show's fan base has grown to the point where Season 8's June premiere drew 3.2 million viewers, a new record and up 5% over the Season 7 premiere.

Media mavens will rightly point out that Dexter isn't much of a mainstream winner when compared with The Walking Dead, which has helped AMC Networks (NASDAQ:AMCX) achieve better-than 15% revenue growth in three of the past six quarters.

Meanwhile, Game of Thrones has proved to be so popular -- drawing as many as 13 million viewers across all channels -- that a surprising number of readers said they would pay a premium if HBO parent Time Warner (NYSE:TWX) would release current-season episodes direct to iTunes for purchase.

Dexter doesn't draw as well as these shows when it comes to viewership numbers. But a winner is still a winner, and Showtime has a long history of developing niche shows that last. Nurse Jackie, starring Edie Falco, has already completed five seasons. Californication, starring David Duchovny, will air its seventh season next year.

Showtime, like HBO, needs these sorts of fan-supported franchises. Shows like Dexter, which enjoyed a standing ovation from the thousands attending the show's final main hall panel at Comic-Con. Ray Donovan is the network's latest try, and it's working so far.

Starring Liev Schreiber as a Boston-born fixer for Hollywood's elite, Ray Donovan drew 1.35 million viewers for its opening episode, the best-ever bow for a new Showtime program and 25% better than Homeland's 2011 debut, the network said in a press release.

Liev Schreiber as Showtime's fixer, Ray Donovan. Sources: The Hollywood Reporter and Showtime.

A second episode did even better, drawing 15% more viewers. Executives have since ordered another season. The message? While HBO and Netflix battle for pay-TV supremacy at about 30 million U.S. subscribers each, Showtime's original programming is drawing growth even as its popular psychopath, Dexter, packs up the kill room. Rarely has CBS looked so interesting.

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