As cast additions continue to be finalized for HBO's "Game of Thrones," Aidan Gillen is the latest to join the epic fantasy series, which is still expected to debut next spring despite re-shoots of the pilot.

Gillen, who played Tommy Carcetti on "The Wire," has signed aboard the series as Littlefinger, an advisor to King Robert Baratheon (Mark Addy) and a master of royal intrigue.

Filming of the 10-episode season is scheduled to start in Northern Ireland later this month. "Game of Thrones" will feature a strong adult tone, reminiscent of the HBO's gritty series "Deadwood" and "Rome."

The series is based on author George R.R. Martins bestselling A Song of Ice and Fire novels, which chronicle a treacherous clash among royal families to secure ultimate power of the vast lands of Westeros.

Martin recently praised Gillen's role on "The Wire."

"Gillen played him brilliantly, painting a vivid picture of a charming, intelligent, well intentioned man slowly seduced by power," Martin said in a LiveJournal post Tuesday. "He should make for a perfect Littlefinger, and I look forward eagerly to seeing what he does with the role."

Casting continues for Season 1's supporting characters. Other recent additions include:

John Bradley-West as Samwell Tarly: "Game of Thrones" marks Bradley-West's first professional audition. Tarly is a noblemans son who is forced into service of the Night Watch.

Miltos Yerolemou as Syrio Forel: Yerolemou is a Shakespearean trained actor with theater, TV and film credits. Syrio is a master of an elegant fencing style known as Water Dancing.

Luke McEwan as Rast: McEwan is a British actor, and a 2009 graduate from the Oxford School of Drama. Rast is a Night Watch recruit.

Jamie Sives as Jory Cassel: Sives' credits include "Doctor Who," the "Clash of the Titans" remake, "Get Him to the Greek." Jory is the commander of an escort of guardsmen who accompany Lord Stark to King's Landing.

Some of the pending cast additions include: Ian McElhinney as Barristan Selmy, and Conan Stevens as Gregor Clegane.

"Game of Thrones" also stars Sean Bean ("The Lord of the Rings") as Eddard "Ned" Stark; Lena Headey ("Terminator: The Sarah Connor Chronicles," "300"), as queen Cersei Lannister; Peter Dinklage ("Threshold") as her cunning dwarf brother Tyrion; Nikolaj Coster-Waldau ("New Amsterdam") as her twin, Jaime; and Jason Momoa ("Stargate: Atlantis") as Khal Drogo.

With key cast members already in place, "Game of Thrones" is poised to re-shoot parts of the pilot, which includes the prologue and scenes with two replacement actresses: Jennifer Ehle as Catelyn Stark, and Emilia Clarke as dragon queen Daenerys Targaryen. The re-shoots don't necessarily point to trouble for the series, however, as the pilot did secure a pickup from HBO on its own merits. Instead, the network seems intent on delivering the best possible adaption of Martin's acclaimed novels.

Tom McCarthy, who earned accolades for his work on 2003's "The Station Agent" and 2007's "The Visitor," directed the pilot based on a script penned by the show's executive producers David Benioff ("Troy," "The Kite Runner") and D.B. Weiss.