Beyond the original NCIS Major Case Response Team characters, NCIS has had many memorable guest stars. Frequently, guests are brought on the show to portray villains or to be wounded or killed in the heat of the action. But sometimes, those who appear in a one-off appearance become series regulars. This is the case for Sean Murray's Timothy McGee and Brian Dietzen's Dr. Jimmy Palmer, the only remaining series regulars who appeared in NCIS season 1.

The Cast Of NCIS
Picture	Character	Actor	First Appearance	Last Regular Appearance
	Leroy Jethro Gibbs	Mark Harmon	Season 1, Episode 1, "Yankee White"	Season 19, Episode 4, "Great Wide Open"
	Dr. Donald "Ducky" Mallard	David McCallum	Season 1, Episode 1, "Yankee White"	Season 20, Episode 22, "Black Sky"
	Anthony "Tony" DiNozzo	Michael Weatherly	Season 1, Episode 1, "Yankee White"	Season 13, Episode 24, "Family First"
	Abigail "Abby" Sciuto	Pauley Perrette	Season 1, Episode 1, "Yankee White"	Season 15, Episode 22, "Two Steps Back"
	Caitlin "Kate" Todd	Sasha Alexander	Season 1, Episode 1, "Yankee White"	Season 2, Episode 23, "Twilight"
	Timothy "Tim" McGee	Sean Murray	Season 1, Episode 7, "Sub Rosa"	-
	Dr. James "Jimmy" Palmer	Brian Dietzen	Season 1, Episode 21, "Split Decision"	-
	Ziva David	Cote de Pablo	Season 3, Episode 1, "Kill Ari Part I"	Season 11, Episode 2, "Past, Present, and Future"
	Director Jennifer "Jenny" Shepard	Lauren Holly	Season 3, Episode 1, "Kill Ari Part I"	Season 5, Episode 19, "Judgment Day Part I"
	Director Leon Vance	Rocky Carroll	Season 5, Episode 14, "Internal Affairs"	-
	Eleanor "Ellie" Bishop	Emily Wickersham	Season 11, Episode 9, "Gut Check"	Season 18, Episode 16, "Rule 91"
	Clayton "Clay" Reeves	Duane Henry	Season 13, Episode 23, "Dead Letter"	Season 15, Episode 22, "Two Steps Back"
	Alexandra Quinn	Jennifer Esposito	Season 14, Episode 1, "Rogue"	Season 14, Episode 24, "Rendezvous"
	Nicholas "Nick" Torres	Wilmer Valderrama	Season 14, Episode 1, "Rogue"	-
	Jacqueline "Jack" Sloane	Maria Bello	Season 15, Episode 4, "Skeleton Crew"	Season 18, Episode 8, "True Believer"
	Kasie Hines	Diona Reasonover	Season 15, Episode 17, "One Man's Trash"	-
	Jessica Knight	Katrina Law	Season 18, Episode 15, "Blown Away"	-
	Alden Parker	Gary Cole	Season 19, Episode 2, "Nearly Departed"	-

Mark Harmon As Leroy Jethro Gibbs

Date Of Birth: September 2, 1951

• Years active: 1970-present

Actor: The Leroy Jethro Gibbs actor was born Thomas Mark Harmon in Burbank, California. The actor gradually came to fame acting in various movie and television roles and had a robust career in both acting and football before his role in the series. That said, NCIS is Mark Harmon's most noteworthy acting role. Many of his acting parts before NCIS were doctor and detective roles, preparing him for the role of Jethro Gibbs. He's also starred in notable films, including his portrayal of Ryan in Freaky Friday alongside Jamie Lee Curtis and Lindsay Lohan.

Notable Movies & TV Shows:

Character: Mark Harmon's character is central to NCIS. He portrayed Special Agent in Charge Leroy Jethro Gibbs, the former team leader of the Major Case Response Team (MCRT) at NCIS Headquarters. As a central character in the NCIS universe, Harmon's character has also appeared in JAG and NCIS: New Orleans.

David McCallum As Dr. Donald "Ducky" Mallard

Date Of Birth: September 19, 1933

• Years active: 1946-2023

Actor: The Ducky actor was born David Keith McCallum in Glasgow, Scotland. In the 1960s, David McCallum gained popularity as Illya Kuryakin in the television series The Man from U.N.C.L.E. The actor was also widely recognized for his role as Dr. Mallard on NCIS, which he portrayed until David McCallum died at 90. He also had roles in films such as The Great Escape (1963) and The Greatest Story Ever Told (1965).

Notable Movies & TV Shows:

Character: David McCallum portrayed Ducky, the beloved medical examiner for the MCRT. His character was full of exciting wisdom that he bestowed on his colleagues, and he was a highly skilled technician in his craft. Following his retirement, Ducky became the NCIS Historian.

Michael Weatherly As Anthony "Tony" DiNozzo

Date Of Birth: July 8, 1968

• Years active: 1990-present

Actor: The Special Agent Anthony DiNozzo actor was born in New York City. Michael Weatherly's most prominent role was Tony DiNozzo in NCIS. However, the actor is known for other television series roles from before and after his stay on the police procedural, including his start on The Cosby Show. After he left NCIS following season 13, he starred as Dr. Jason Bull in the courtroom drama Bull. Michael Weatherly will reprise the role of Anthony DiNozzo in NCIS: Tony & Ziva.

Notable Movies & TV Shows:

Character: In NCIS, Anthony D. "Tony" DiNozzo Junior was the Senior Field Agent for Gibbs' team. He was second-in-command to Gibbs and led the team on rare occasions when he was absent. Tony eventually departed NCIS to raise his daughter Tali but appeared in NCIS season 21.

Pauley Perrette As Abigail "Abby" Sciuto

Date Of Birth: March 27, 1969

• Years active: 1994-2020

Actor: Pauley Perrette is an actor and singer born in New Orleans, Louisiana. She began acting on the ABC Afterschool Specials in 1994 and was a server at Cafe Nervosa in two episodes of Frasier season 4. Perrette's most substantial role was in NCIS, portraying the forensic scientist Abby Sciuto. She has also appeared in noteworthy films such as Almost Famous (2000) and The Ring (2002). Before her NCIS stint, Perrette was in a Los Angeles all-girl band called Lo-Ball.

Notable Movies & TV Shows:

Character: Pauley Perrette portrayed Abby Sciuto, the team's chief forensic scientist. She provided the team with crucial intel on forensics, ballistics, and genetics, all while blaring hardcore or heavy electronic music and decked out in goth makeup and attire.

Sasha Alexander As Caitlin "Kate" Todd

Date Of Birth: May 17, 1973

• Years active: 1997-present

Actor: The Caitlin Todd actor was born Suzana Drobnjakovic in Los Angeles, California. Before her role on NCIS, Sasha Alexander portrayed Gretchen Witter in season 4 of Dawson's Creek. After NCIS, Alexander starred in the crime drama Rizzoli & Isles and was a regular character in Shameless. After NCIS, she also appeared in noteworthy films, including Jim Carrey's Yes Man (2008) and He's Just Not That Into You (2009).

Notable Movies & TV Shows:

Character: In NCIS, Sasha Alexander portrays Special Agent Kate Todd. Alexander's character starts as a Secret Service agent in season 1, episode 1, "Yankee White," but s Gibbs' team at the end. The character was brutally murdered in the final moments of season 2.

Sean Murray As Timothy McGee

Date Of Birth: November 15, 1977

• Years active: 1991-present

Actor: Sean Harland Murray was born in Bethesda, Maryland, at the Bethesda Naval Hospital. When he was 11, Sean Murray was an extra in My Blue Heaven starring Steve Martin and Joan Cusack. In 1993, Sean Murray made his first motion picture appearance playing Thackery in Disney's Hocus Pocus. Before stepping into the role of McGee on NCIS, Murray appeared in JAG seasons 4 and 6 as Ensign Terry Guitry and Danny Walden. Murray's career is dominated by his two decades on NCIS. He is the stepson of NCIS creator Donald P. Bellisario.

Notable Movies & TV Shows:

Character: Sean Murray portrays NCIS Special Agent Timothy McGee in the series. McGee was initially assigned to the Norfolk Naval base but ed the Gibbs team as a probationary agent after providing critical intel in NCIS season 1. McGee adds valuable computer skills to the team, with degrees from Johns Hopkins University and MIT.

Brian Dietzen As Dr. James "Jimmy" Palmer

Date Of Birth: November 14, 1977

• Years active: 2002-present

Actor: Brian Dietzen was born in Barrington, Illinois, and moved to Colorado when he was young. His two-decade stint on NCIS dominates his career, but Brian Dietzen had a few other roles before being cast as Jimmy Palmer. Dietzen portrayed the drummer Owen in My Guide to Becoming a Rock Star and Eddie in the 2003 film From Justin to Kelly. Since acting on NCIS, Dietzen has co-written several episodes, making him one of the NCIS stars who expanded their roles in the series.

Notable Movies & TV Shows:

Character: Jimmy Palmer started as Ducky's medical assistant toward the end of NCIS season 1. After Dr. Mallard retires, Jimmy ultimately becomes the team's chief medical examiner, responsible for performing the team's autopsies.

Cote de Pablo As Ziva David

Date Of Birth: November 12, 1979

• Years active: 1994-present

Actor: The Ziva David actor was born María José de Pablo Fernández in Santiago, Chile. Cote de Pablo's breakout role was her Ziva character on NCIS. Before that, she had just a few features on television, including a regular role in The Jury. Since her time on the series, Cote de Pablo has been featured in several movies, including The Last Rites of Ransom Pride (2010) and The 33 (2015). The actor will reprise her Ziva role in the spinoff NCIS: Tony & Ziva.

Notable Movies & TV Shows:

Character: The Ziva character is introduced as a Mossad officer at the beginning of season 3 and has robust ties to Israel. She is the half-sister of Ari Haswari and the daughter of Mossad Director Eli David. Ultimately, she s Gibbs' team before Ziva fakes her NCIS death in season 13.

Lauren Holly As Director Jennifer "Jenny" Shepard

Date Of Birth: October 28, 1963

• Years active: 1984-present

Actor: Lauren Holly was born in Bristol, Pennsylvania. She's had a massive career with noteworthy roles dating back to the 1990s. Holly's breakout role was the small-town sheriff Maxine Stewart on CBS's Picket Fences. In 1994, Holly was Mary in Dumb and Dumber with Jim Carrey, to whom she was briefly married. She also appeared in Chicago Hope season 6 alongside NCIS' Leroy Jethro Gibbs and Leon Vance stars Mark Harmon and Rocky Carroll. She also voiced Chihiro's mother in the English version of Hayao Miyazaki's Spirited Away.

Notable Movies & TV Shows:

Character: Lauren Holly portrayed NCIS Director Jennifer Shepard on NCIS. She was the former partner and lover of Special Agent in Charge Leroy Jethro Gibbs. She was a capable yet empathetic director who worked with the MCRT team instead of regulating them. She is murdered at the end of NCIS season 5.

Rocky Carroll As Director Leon Vance

Date Of Birth: July 8, 1963

• Years active: 1989-present

Actor: The Leon Vance actor was born Roscoe Carroll in Cincinnati, Ohio. Rocky Carroll's breakout role was as Joey Emerson in Roc, and he was also known at the time for playing Dr. Keith Wilkes in the CBS medical drama Chicago Hope. He played a ing role in Crimson Tide and landed it big in 2008 when he became NCIS Director Leon Vance alongside his Chicago Hope co-star Mark Harmon. Carroll credits Harmon for his landing the role. Leon Vance's NCIS director role extends to the other NCIS location-based spinoff shows.

Notable Movies & TV Shows:

Character: In the police procedural, Rocky Carroll portrays NCIS Director Leon Vance. Vance takes over after Director Shepard is killed in a shoot-out in season 5. He oversees the MCRT at NCIS Headquarters, and the teams in all the NCIS spinoff shows.