Unlike his tough, seemingly always together partner, Ryan is a little more of a clutz, but still a very skilled detective. He tends to put his foot in his mouth, eliciting a slap across the head from Esposito or a glare from Beckett, and drop or bumble things. One time he pushed off too hard while sitting in his rolling desk chair and Esposito had to grab the chair's arm to keep Ryan from flying across the precinct. Nevertheless, he is fiercely loyal to Beckett and Esposito.
Ryan is also more impressionable than Esposito. In Close Encounters of the Murderous Kind, he admits he always suspected that a relative had been abducted by aliens, just as Castle thinks he and Beckett were, and in The Fast and the Furriest he joins Castle in trying to prove to Esposito and Beckett that Big Foot could be responsible for the death of a college student. He frequently finds himself siding with Castle against the more skeptical Esposito and Beckett in their friendly debates over Castle's off-the-wall theories.
Before joining homicide, Ryan worked with the narcotics division of the NYPD (around 2003 when the legend Cavalo started to circulate).His most significant work was going undercover for 14 months as Fenton O'Connell to infiltrate an Irish drug gang. After being gone for seven years, Ryan resurrects Fenton in The Wild Rover to solve the murder of a baker who was acting as an FBI informant.
Family and Romantic Life
He is in a happy relationship with a sweet young woman named Jenny Ryan, who, as Esposito says, has him "whipped." As of Little Girl Lost, they had been dating for two weeks. In Nikki Heat, he proposes to her, saying she will make him the happiest man in the world, and she accepts. They marry in Til Death Do Us Part.
While undercover as a narcotics cop, Ryan fell for bar owner Siobhan O'Doul, but had to leave her when it got too dangerous for him. They reunite in The Wild Rover when Siobhan's life is at risk for being an FBI informant and in order to save her, Ryan has to take down the leader of the gang he infiltrated.
One of his previous girlfriends was into vampirism, which eventually caused him to break up with her.
Seamus plays him like he has two older sisters "so Ryan's always been comfortable with his feminine side..." In Once Upon a Crime, he tells Beckett that an older sister used to read him the Little Red Riding Hood fairy tale when he was younger.
In season 5, starting with Secret Santa, Ryan and Jenny begin trying to have a baby and in The Wild Rover, Jenny tells him she is pregnant. In Under Fire, Jenny gives birth to a baby girl, who they name Sarah Grace, after Jenny's grandmother. Had the baby been a boy, they would have named him Javier, after Esposito.
- His colleagues poke fun of him because of his nickname of Honeymilk, which comes from the warm milk infused with honey that his girlfriend and eventual wife, Jenny, makes him to help him sleep at night.
- To Esposito's horror, he reveals that he got the couch in his apartment on which he and Esposito frequently sit to play video games, from the corner of 54th and Lexington Avenue, where someone had abandoned it.
- Is a fan of the book Eat, Pray, Love
- Was once invited to become a male stripper by a booking agent who assured him that the Twilight look was in.
- His girlfriend/fiancee/wife Jenny is played by Seamus Dever's real-life wife Juliana Dever.
- Has a dream of buying a winery if he ever wins the lottery since he and Jenny visited one on their first vacation together.
- Ryan is also a huge Elvis fan. His mother was obssesed with his music.
- His badge number is 42344.
- He was a fan of the children's character Curious George as a kid and therefore wanted a pet monkey
- "Interview with Seamus Dever" Movie Mikes, written by Mike Gencarelli, posted January 24, 2011
- "Interview: Castle Co-Stars Nathan Fillion & Stana Katic The Futon Critic, written by Jim Halterman, posted 11/15/2010
- Vampire Weekend, episode 2.6
- Comic-Con 2011: Castle interviews with Nathan Fillion, Seamus Dever, Jon Huertas, Molly Quinn, and Executive Producer Laurie Zaks by Dave Trumbore, Collider.com, posted July 27, 2011
- Hell Hath No Fury, episode 1.4
- Almost Famous, episode 3.7
- Lucky Stiff, episode 3.14
- After the Storm
- The Fast and the Furriest