The main character, played by Jennifer Garner. She's a spy for the CIA inside SD-6. Her fiance, Danny Hecht, was killed after she told him about working for SD-6. At the time she believed that it was part of the CIA. She later found out that it was an enemy of the USA. Her cover is that she works for a bank, Credit Dauphine. The SD-6 offices are located beneath the bank.
Sydney's father, played by Victor Garber, who also is a CIA agent in SD-6. His wife was killed in a car accident, but in later episodes we find out that she was a KGB agent, and that she is still alive today. Jack is one of the few agents who know the truth about SD-6.
Sydney's partner at SD-6, played by Carl Lumbly. Sydney assumes that he does not know the truth about SD-6. In later episodes he begins to suspect that Sydney isn't just working for SD-6. His cover is that he works for a bank, Credit Dauphine.
The head of SD-6, played by Ron Rifkin. He cares for Sydney like she was his own daughter, and is now showing some emotion about ordering her fiance killed, since she did not report his wife to security section when revealed that she knew of SD-6. Has suspected Sydney of being a mole more than once, and has almost had her killed a few times.
SD-6's tech guy, played by Kevin Weisman. We assume that he doesn't know the truth. He not realy adept with words, and always trys to make small talk during briefings. He has designed all of the gadgets used during missions, most of which are pure genius.
Sydney's CIA handler, played by Michael Vartan. Despite his efforts, he is definitely too emotionally attached to Sydney, and has crossed the line more than a few times in order to save her.
Sydney's nosy reporter friend, played by Bradely Cooper. He is curious about why the police didn't investigate Danny Hecht's (Sydney's fiance) death more closely. He eventually learns too much, and ends up on almost getting killed a few times. He originally thought Sydney worked at a bank, Credit Dauphine, but later found out that she works for SD-6.
Sydney's best friend and roomate, played by Merrin Dungey. She moves in with Sydney after Danny is killed, and eventually breaks up with her fiance after find out he was cheating on her. She thinks Sydney works at a bank, Credit Dauphine.