Alias is an American action/drama television series created by J.J. Abrams which was broadcast on ABC from September 30, 2001 to May 22, 2006, spanning five seasons. It starred Jennifer Garner as Sydney Bristow, an agent who had been tricked to believe she was working for the U.S. government but had, in fact, been working for a criminal organization named the Alliance of Twelve. Upon learning this Sydney became a double agent for the real CIA, feeding information from SD-6 to them.
Though the cast remained largely similar throughout the series, several new characters were brought in for the final season. Throughout the series regular characters were Jack Bristow (Victor Garber), Sydney's father who coincedentally also was a double agent for the CIA working in SD-6. Arvin Sloane (Ron Rifkin), the head of SD-6 and Sydney's enemy throughout the series. Michael Vaughn (Michael Vartan) was Sydney's CIA handler before they engaged in a romantic relationship, and Marcus Dixon (Carl Lumbly) was Sydney's field partner at SD-6. Sydney's friends Will Tippin (Bradley Cooper) and Francie Calfo (Merrin Dungey) were featured, concerned about Sydney throughout the first two seasons but were less involved thereafter. Eric Weiss (Greg Grunberg) was another CIA agent with Vaughn, and Marshall Flinkmann (Kevin Weisman) was a computer genius working for SD-6. Sydney's mother Irina Derevko (Lena Olin) was a recurring nemesis, as was Julian Sark (David Anders) a villainous turncoat who was willing to give up any or all information to save him from imprisonment or torture.
Other characters were later into the series. Lauren Reed (Melissa George) married Vaughn after Season 2 when Sydney disappeared for two years, but turned out to be working for The Covenant and Sydney killed her. Sydney's half sister Nadia Santos (Mia Maestro) played a role in the later series, but perished at the hands of her father, Arvin Sloane, due to his obsession with Milo Rambaldi. In the fifth season several new recruits were made to the CIA's branch known as Authorized Personnel Only; Rachel Gibson (Rachel Nicols) and Thomas Grace (Balthazar Getty). Assisting APO was Renée Rienne (Élodie Bouchez), a French operative, and working against them was Kelly Peyton (Amy Acker) who worked with Prophet 5.