Rigg will play Lady Olenna Tyrell — also known as "The Queen of Thorns" — who is the grandmother of Margaery and Loras Tyrell and is, in many ways, the true leader of their powerful family. Crook will play Orell, a "warg" or "skinchanger," with the ability to enter the mind of an animal and control its actions.

Other actors who will join the upcoming season include Clive Russell, Nathalie Emannuel, Kerry Ingram, Paul Kaye, Thomas Brodie-Sangster, Ellie Kendrick, Richard Dormer, Kristofer Hivju, Philip McGinley, Tara Fitzgerald, Tobias Menzies and Anton Lesser.

Based on the bestselling fantasy book series by George R.R. Martin, "Game of Thrones," according to HBO, "is an epic drama set in the world of Westeros, where ambitious men and women of both honor and ill-repute live in a land whose summers and winters can last years. The Emmy and Golden Globe-winning fantasy series concluded its ten-episode second season in June, with the third season scheduled to launch in 2013."

Rigg won the Tony Award in 1994 for her performance in Medea and was nominated for her performances in The Misanthrope and Abelard and Heloise. Visit her page at the Playbill Vault.

Crook was nominated for the Tony Award in 2011 for his performance in Jerusalem. He has also been seen on Broadway in The Seagull. Visit his page at the Playbill Vault.

For more information on "Game of Thrones," click here.