As an African-American Muslim FBI agent, Darwyn was assigned to infiltrate an Islamist terrorist sleeper cell.
Saad bin Safwan (played by Oded Fehr) is the charismatic leader of the terrorist cell.
Following this, he fought alongside the Bosnian mujahideen in Bosnia (where he met and saved his right-hand man, Ilija Korjenić), and then fought alongside the Taliban in Afghanistan after he met Osama bin Laden, and later run Afghan training camp for Al-Qaeda.
Ilija Korjenić (played by Henri Lubatti) is a Bosnian-Muslim who became a terrorist after his entire family was killed in the Bosnian Genocide.
Gayle Bishop (played by Melissa Sagemiller) is a single mom who falls in love with Darwyn.
She is kidnapped and killed in the last episode by Mina, on orders from high up, as retribution for turning Darwyn in as a suspected terrorist in season one.
Christian Aumont (played by Alex Nesic) is a former skinhead from Paris who converted to Islam after falling in love with a Moroccan Muslim.
It was revealed that his wife, Zohra, was pregnant, and that since he was going to kill innocents she couldn't deal with being associated with him anymore, even for their child.
Thomas "Tommy" Allen Emerson (played by Blake Shields) is the blonde-haired, blue-eyed son of two liberal college professors from Berkeley, California.
Patrice Serxner (played by Sonya Walger) is the FBI agent who takes over Fuller's position after he is killed.
Salim (played by Omid Abtahi) is a young Iraqi-born Muslim who was brought up in the UK as a British Iraqi after his family left Iraq during the Iran–Iraq War.
Coincidentally, Abtahi would later go on to play another (unrelated) gay Muslim man also named Salim in the 2017 series American Gods.
Benito 'Benny' Velasquez (played by Kevin Alejandro) is a Latino gang member who converted to Islam and befriended Darwyn while in prison.
Warren Russell (played by Jay R. Ferguson) is Darwyn's latest supervisor, who replaces Serxner after she is killed in Sudan.
Young and inexperienced, he got the job only because his uncle is a powerful Deputy Director of the FBI, and his incompetence causes him to clash with Darwyn.
Abdullah "Bobby" Habib (played by Grant Heslov) was a member of the original Los Angeles sleeper cell and Gayle's next-door neighbor.
He immigrated with his mother at Chicago, Illinois, at age fifteen, after his father, who was a colonel in the Egyptian Army was executed for participation in the murder of the president Anwar al-Sadat.
The Librarian (played by Albert Hall) is a "lifer" in prison where he preaches radical Islam to fellow inmates, preparing them to join terrorist groups upon their release.
Eddy Pangetsu (played by Jeff Mallare) is an Indonesian-American biochemical student at USC who moved to America when he was young.
Jamal (played by Jerrith J. Merz) is an imprisoned Islamic extremist who first appeared at the beginning of the episode "Scholar".
Ken Walls (played by John Siciliano) is a former mujahid who fought in Bosnia, earning him Ilija's respect.
When the United States offered rewards for information on al-Qaeda and the Taliban, Khashul's family was accused by a personal enemy.
Khashul goes to Ken Walls' facility, now run by the cell, hoping to join the insurgency in Iraq.
Ilija is greatly angered when the terrorists offer him a position in Canada after he kills her, as it would have made her death unnecessary.
Salim calls Hassani a thief and, in accordance with his strict interpretation of sharia law, cuts off his hand.
Robert "Bob" McNeil (played by Chris Mulkey) is one of the CIA interrogators who questions Farik at Gitmo.
Khalid Noor al-Dibb (played by Aasif Mandvi) was the leader of the second Los Angeles sleeper cell.
Jason (played by Michael Rady) is a gay man who Salim starts a relationship with after the two meet in a health club.
Abu Amin Mussa, better known by his alias Karrar Bashir al-Abbani (played by Saïd Taghmaoui) is a Muslim terrorist who Farik has replace Darwyn as the new leader of the second Los Angeles sleeper cell.
When the cell's attack starts, Darwyn reveals that he's a member of the FBI and tells Karrar to surrender.