(In order of number of episodes)
- 1 Sidney Perlmutter
- 2 Pi
- 3 Dr. Carter Burke
- 4 Jim Beckett
- 5 Jenny Ryan
- 6 Josh Davidson
- 7 Tom Demming
- 8 Tory Ellis
- 9 Gina Cowell
- 10 Ashley
- 11 Robert Weldon, NYC Mayor
- 12 Rachel McCord
- 13 Meredith
- 14 Will Sorenson
- 15 Mike Royce
- 16 Hal Lockwood
- 17 Dr. Holloway
- 18 Gilbert Mazzarra
- 19 Detective Roselyn Karpowski
- 20 Dr. Clark Murray
- 21 Judge Markway
- 22 Grant "Sully" Sullivan
- 23 Triple Killer
- 24 Beau Randolph
- 25 West Side Wally
- 26 Chet
- 27 Real life writers
Sidney PerlmutterArye Gross
A curmudgeonly Medical Examiner who makes no secret of the fact that he does not like Castle.
He appears in the following episodes:
- The Double Down
- When The Bough Breaks
- Famous Last Words
- Kill The Messenger
- Suicide Squeeze
- Food to Die For
- Pretty Dead
- Undead Again
- The Final Frontier
- Scared to Death
- The Fast and the Furriest
- Need To Know
Played by: Myko Olivier
Alexis' New Age, fruitarian boyfriend when she returns from a summer trip to South America. He appears in the season 6 episodes:
Played by: Michael Dorn
An NYPD psychologist who Beckett sees for counseling after being shot. He appears in:
Played by: Scott Paulin
Kate Beckett's father. He appears in:
Played by: Juliana Dever
Detective Kevin Ryan's sweet girlfriend, fiancee, and finally wife. She appears in:
Played by: Victor Webster
A motorcycle-riding cardiac surgeon who Beckett dates for about a year. He appears in:
Played by: Michael Trucco
A handsome robbery detective whom Kate Beckett dates briefly. He appears in the last 4 episodes of season 2.
Played by: Maya Stojan
An intelligent and attractive NYPD Tech officer. She appears in:
Played by: Monet Mazur
Castle's publisher and second ex-wife. She appears in:
She also appears in a picture on Castle's phone in Poof, You're Dead in season 3.
Played by: Ken Baumann
Alexis's first serious boyfriend and first love. He appears in:
Robert Weldon, NYC Mayor
A friend and fan of Castle's books who allows him to shadow Beckett. Castle has nicknamed him "Big Cheese" and he occasionally joins him for poker at his apartment. Joseph Phillips plays him in 2 episodes, and Derek Webster in 1. He appears in:
Played by: Lisa Edelstein
Beckett's tough, but empathetic partner during her short tenure with the U.S. Attorney General's office in Washington, DC. She appears in:
Played by: Darby Stanton
Castle's first ex-wife and Alexis' mother who Castle calls the "Deep Fried Twinkie" because of her crazy, over-dramatic ways. She appears in
Played by: Bailey Chase
An attractive FBI Agent and ex-boyfriend of Beckett's who she dated before she met Castle. He appears in season 1 episodes:
Played by: Jason Beghe
Detective Kate Beckett's former training officer, and an early love. He appears in:
Played by: Max Martini
A trained assassin who worked under the same mad who ordered the hit on Johanna Beckett and also kills Detective Raglan, who originally investigated her murder. He appears in season 3 episodes
Played by: Phil LaMarr
A psychologist with the NYPD. He appears in season 2 in:
Played by: Danny Nucci
A detective friend and former colleague of Esposito's. He appears in season 2 in:
Played by: Diana-Maria Riva
A colleague of Beckett's at the precinct. She appears in season 2 in:
Played by: Robert Picardo
A forensic pathologist known as "Dr. Death" and friend of Castle's. He appears in:
Played by: Dan Castellaneta
A golfing friend of Castle's who periodically joins him for poker games at his apartment. He appears in season 1 episodes:
Grant "Sully" Sullivan
Played by: Joshua Bitton
The rookie NYPD homicide detective who takes Beckett's desk at the 12th when she takes a job in Washington, DC. He appears in:
Played by: Michael Mosley
A sadistic serial killer who killed 6 women four years before Castle and Beckett met, disappeared, then returns to killing. He appears in:
Played by: Jordan Belfi
The sleazy producer of a series of college girl videos. Appears in 2 episodes.
West Side Wally
Played by: Loren McCraley
A homeless man who helps Beckett and her team with cases. Appears in 2 episodes.
Martha's unseen boyfriend who dies early in season 3.
Real life writers
Stephen J. Cannell, Michael Connelly, James Patterson, and Dennis Lehane all appear as themselves and friends of Castle's. Over periodic games of poker at Castle's apartment, they help Castle figure out murder cases that have he and Beckett stumped. Cannell appears in the series premiere and the first and final episodes of season 2, Patterson in the series premiere and final episode of season 2, and Connelly in the first and final episodes of season 2.
(alternate list restored below - need to make sure all this info is incorprotated above)
- Sidney Perlmutter (Arye Gross) - The curmudgeonly Medical Examiner who doesn't like Castle very much. Appears in 12 episodes.
- Jim Beckett Scott Paulin) - Kate Beckett's lawyer father. Appears in 8 episodes.
- Tory Ellis (Maya Stojan) - An attractive CSU Tech. Appears in 6 episodes.
- Pi (Myko Olivier) - Alexis' fruitarian boyfriend. Appears in 6 episodes.
- Dr. Carter Burke Michael Dorn) - The NYPD psychiatrist Beckett sees to treat her post-traumatic stress disorder. Appears in 5 episodes)
- Jenny Ryan Juliana Dever) - Ryan's girlfriend/fiancee/wife. Appears in 5 episodes.
- Josh Davidson Victor Webster) - The heart surgeon Beckett dates briefly. Appears in 4 episodes.
- Tom Demming Michael Trucco) - A robbery detective Beckett dates at the end of season 4. Appears in 4 episodes.
- Gina Cowell Monet Mazur) - Castle's second wife, his girlfriend briefly, and his publisher. Appears in 3 episodes.
- Ann Hastings (Valerie Azlynn) - NYPD beat cop who Beckett & Castle discover moonlights as a crime-fighting vigilante. Appears in 3 episodes.
- Ashley Ken Baumann) - Alexis' first serious boyfriend. Appears in 3 episodes.
- Triple Killer/3XK (Michael Mosley) - A sadistic serial killer who repeatedly eludes capture. Appears in 3 episodes.
- Rachel McCord (Lisa Edelstein) - Beckett's partner when she worked in Washington, DC. Appears in 3 episodes.
- Meredith Darby Stanchfield) - Castle's first wife and Alexis' mother. Appears in 2 episodes.
- Will Sorenson Bailey Chase) - An FBI Agent who Beckett dated for 6 months. Appears in 2 episodes.
- Jordan Shaw (Dana Delany) - An FBI Agent and profiler who Castle admires. Appears in 2 episodes.
- William Bracken (Jack Coleman) - The U.S. Senator who ordered Beckett's mother's murder. Appears in 2 episodes.
- Roselyn Karpowski (Diana Maria Riva) - One of Beckett's detective colleagues. Appears in 2 episodes.
- Judge Markway (Dan Castellaneta) - A judge with whom Castle occasionally plays golf. Appears in 2 episodes.
- Mike Royce (Jason Beghe) - Beckett's training officer from when she started with the NYPD. Appears in 2 episodes.
- Mayor Robert Weldon (Joseph C. Phillips/Derek Webster) - Mayor of New York City, from whom Castle has permission to shadow Beckett. Joseph Phillips plays him in 2 episodes, and Derek Webster in 1.
- Dr. Clark Murray (Robert Picardo) - Known as "Dr. Death", Castle and Lanie enlist his help with cases that relate to Beckett's mother's murder. Appears in 2 episodes.
- Grant "Sully" Sullivan (Joshua Bitton) - The sloppy homicide detective who takes Beckett's desk when she leaves to work in DC. Appears in 2 episodes.
- Gilbert Mazzarra (Danny Nucci) - A detective friend of Esposito's. Appears in 2 episodes.