[6] He describes Castle as being "a bit of a douche" with a Peter Pan syndrome stemming from a lack of a "real male adult role model in his life".

[6][7] Andrew Marlowe explained that he designed Castle's character as one that presents a "storytelling point of view" as a counterpoint to Beckett's evidence-based police work.

He was further inspired to become a writer when a man (later revealed to be the father he never knew) handed him a copy of Ian Fleming's Casino Royale at the New York Public Library when he was ten years old.

[16] Castle and Gina became involved again, briefly, when she spent a summer with him in the Hamptons supervising his second Nikki Heat novel, but they soon ended their relationship.

Castle also plays regular poker games with fellow authors James Patterson, Stephen J. Cannell, Michael Connelly, and Dennis Lehane.

When Cannell died in 2010, a fictional mystery writer was invited by Castle to the game, but a seat was left empty in their friend's honor.

In the fifth season, Castle finally meets his father (portrayed by James Brolin), whom he learns is a spy when he helps him rescue Alexis when she was kidnapped.

At the end of the final fifth-season episode, Castle proposes marriage to Beckett just as she prepares to reveal her decision on a Washington, DC job offer.

They are finally married during the seventh season in a private wedding with their family, taking place at Castle's house in the Hamptons.

In the eighth and final season, Beckett estranges herself from Castle in order to protect him from LokSat, a deadly mastermind whom she's after, although they are married still and very much in love.

His other books include Death of a Prom Queen, Flowers For Your Grave, Hell Hath No Fury, A Skull at Springtime, At Dusk We Die, When It Comes to Slaughter, and A Rose for Everafter.

In the present of the episode, Castle is confronted by a similar case and finally gets to learn the truth of what happened that day and personally stop a serial killer of an unknown, but presumably large, number of murdered women.

Amongst the useful skills Castle (and to some extent, partner-in-crime Alexis) have acquired are lock picking, safe cracking, fencing, and a basic grounding in forensic science and criminal psychology.

Because he's a writer, although he notoriously shirks "boring paperwork," his ability to speed-read allows him to sift through information faster than most of the precinct (a skill Gates puts to use when hunting for a bomber) and he retains almost everything he reads, especially when it comes to case files (making him the closest approximation to an expert when Jerry Tyson, aka 3XK, returns in Season 7 after stealing his entire case file in Season 6).

Although shaken by an encounter with the serial killer who inspired his writing interest, Castle accepts the award and dedicates it to his family and friends as he recognizes that, without them, he wouldn't have won it.

Unsatisfied with what he considers a boring resolution to the case, Castle convinces Beckett to continue the investigation, and winds up discovering deeper layers to the crime.

By the end of the pilot, Castle enters into a working relationship with Beckett under the pretense of conducting research for his new series of "Nikki Heat" novels.

Although he is a proficient marksman (secret until Beckett bets with him on the practice range), he works the cases wholly unarmed (with a few rare, isolated exceptions).

While his status as a consultant generally allows him to participate in the 'fun' parts of detective work without worrying about the more tedious details such as paperwork, the team puts him in situations where the criminals request no police involvement, such as to drop off a ransom.

He once speculated that a surgeon had been killed for his involvement in an organ-smuggling ring before they discovered that he was wanted for plastic surgery he had performed for someone in witness protection.

Initially portrayed as jocular and immature, such as having a bulletproof vest made up for himself that says "WRITER" rather than "POLICE", Castle's character deepens as the series progresses.

He then offers to terminate his partnership with Beckett after she was forced to shoot the real killer, revealed to be a contract assassin silent about his employer.

In "Pandora" (S04 E15) and Linchpin" (S04 E16), the investigation of a murder leads Castle and Beckett to reunite with Sophia Turner (Jennifer Beals), a CIA operative on whom he based a major character.

However, Sophia turns out to not only be part of the plot but is actually a KGB mole who infiltrated the CIA only to be left on her own when the Soviet Union collapsed.

After nearly dying in a confrontation with the killer and quitting the police force, Beckett comes to Castle's apartment, telling him she could only think of him while on the verge of death and then they later kiss passionately.

In the season six episode "Veritas" (S06 E22), after Beckett is framed for murder by the man who had ordered the death of her mother, Castle works to protect her.

After being restored to his position in the police department, Castle is finally able to bring down old enemy Jerry Tyson, aka serial killer 3XK during "Resurrection" (S07 E14) and "Reckoning" (S07 E15).

The investigation leads them to discover a serial killer who has been operating for at least thirty years with an unknown number of victims, all people who won't be missed.

Castle is forced to fatally shoot the killer in self-defense with Beckett's gun and brings closure to his victims though the incident leaves him shaken.

It was then officially acknowledged that the Castle book series was indeed entirely written by a ghostwriter and that established screenwriter Tom Straw wrote the first seven.