BEWARE OF SPOILERS. Due to the nature of the show, with its many Walking Spoiler characters, twists, and turns, the only spoilers whited out are those for the current season "24: Live Another Day". Proceed with caution!
The leader of Second Wave, an Islamic terrorist group. He intended on detonating a nuclear warhead in Los Angeles.
- Disc-One Final Boss: Ali halfway through Day 2.
- Even Evil Has Loved Ones: Jack breaks him by faking the execution of his family. Watching it seemingly happen absolutely devastates him.
- Faking the Dead: Syed pretended to die by setting someone wearing his clothes on fire.
- He Knows Too Much: Killed by one of the mercenaries, but less to cover up the conspiracy as to maintain his leverage.
- Real Men Love Jesus: Ali took the time to pray at a mosque just before launching his attack.
- Unwitting Pawn: Of Peter Kingsley.
The sister of Kate Warner who is really helping Ali detonate a nuke in LA.
- Brainwashed and Crazy: Kate called Marie this.
- Cain and Abel: The Cain to Kate's Abel.
- The Dragon: To Syed Ali.
- Emotionless Girl: By the end of the season, she's become one.
- Even Evil Has Loved Ones: Subverted.Marie: I killed Reza... and I loved him. What makes you think I would care about you and Dad?
- The Mole: For Second Wave and Syed Ali.
- Psychopathic Manchild: Kate considered Marie's motives childish.
- The Quiet One: Marie was very vocal about her political views until she was radicalised. Then she became very quiet.
- Rape as Backstory: A deleted scene reveals that while she and her family were living in Saudi Arabia, a Saudi girl who was a close friend of hers was raped by an American soldier.
- Smug Snake: Jack can tell right away that Marie isn't the type to endure true torture.
- Start of Darkness: The death of Marie's mother.
- Ungrateful Bastard: Kate called Marie this.
- The Vamp: Marie seduced a man to get the nuke's final component.
An American terrorist ring leader who was responsible for bombing CTU. He was a pawn for the Second Wave.
- Character Death: He kills himself rather than be captured by CTU.
- Driven to Suicide: When Jack breaks into his compound to arrest him, Wald shoots himself.
- Even Evil Has Standards: He has problem bombing CTU to fight the federal government, but draws the line at a nuclear attack that will kill a million innocent Americans.
- Right-Wing Militia Fanatic
- Unwitting Pawn: To Nina Myers and Syed Ali.