As a child, Horatio was a victim of domestic violence (his mother was killed by his father), which accounts to his comparatively extreme reactions in abuse cases. Caine then worked in New York City as detective with the NYPD. It was there that he killed his father. In 1995, while on the job, he was stabbed while investigating a case in which children were locked in closets while their parents were murdered. The perpetrator, Walter Resden, harbored a deep grudge against Caine, collecting the blood from the stabbing and preserving it for 10 years in order to frame him for the murder of Caine's girlfriend, Rachel Turner.
After his arrival in Florida, Horatio joined the Miami-Dade Police as a homicide detective but later transferred to the bomb squad, where he was mentored by Al Humphries, an older cop whom Caine highly respected and considered a good friend; Humphries was later killed after accidentally triggering a bomb he was attempting to disarm (Losing Face). Horatio worked undercover as "John Walden" in Pensacola, Florida for sometime during the early 1990s (this is the date given on the show, despite the fact it was previously understood on the show that Horatio worked in New York until at least 1995). During his time there, he dated a woman he believed to be named Julia Eberlie, and the two conceived a son named Kyle. Horatio would not be aware of Kyle's existence for another sixteen years. Sometime later he returns to Miami and to being a detective, in "Out Of Time" he references previously working on the bomb squad. Finally, Caine moved to the Crime Lab, accepting a promotion to lieutenant, which earned him the animosity of Sergeant Rick Stetler, who was also vying for the rank. When veteran CSI Megan Donner went on personal leave following the death of her husband, Horatio became the permanent head of the lab.
A superb marksman, Caine doesn't hesitate to use deadly force when needed. He is also an ardent advocate of the death penalty for particularly heinous crimes, and doesn't think twice about threatening suspects with it in such cases. In the first two seasons, Caine carried a Beretta Cougar on the job. Since the beginning of season three, he has been shown carrying a SIG-Sauer P229. He is very insistent on gun maintenance, especially since team member Tim Speedle was killed in a shootout after his gun misfired because of the lack of maintenance. In fact, one of the reasons for Caine's nearly on-the-spot selection of Officer Ryan Wolfe as Tim Speedle's replacement (in episode 303, "Under the Influence") is Wolfe's compulsive care of his firearm due to OCD.
He is later forced to fire Wolfe, as the younger CSI compromised himself during the course of the investigation due to his gambling debts and lack of honesty regarding the situation (episode 522, "Burned"). Wolfe also previously violated protocol. Caine indicates a willingness to allow Wolfe to redeem himself, however, and possibly allow him to return to the team after reviewing all the files from his previous cases (episode 523, "Kill Switch").
At the end of Season 2 (episode 223, "MIA/NYC — Nonstop"), Caine travels to New York City in pursuit of a murder suspect and meets Detective Mac Taylor and his team, inaugurating the first season of CSI: NY. Caine later reunites with Detective Taylor and the New York CSIs to track down and arrest the murderer, Henry Darius, who would be extradited to Florida to face the death penalty (CSI: Miami episode 407, "Felony Flight," CSI: NY episode 207, "Manhattan Manhunt"). This appearance would make Horatio Caine the first character to appear at least once in all three CSI shows.
At the end of the season 6 finale, Horatio is shot. It appears as though he is dead, but in behind the scenes video, it's said Horatio's death was faked so he can go after Ron. David Caruso says, "Horatio designed a staging of an event that will free him up to go after this man with a different license." This was later proven true as Horatio was seen alive in "Resurrection, Part 2".
He has many recurring enemies throughout the series, from serial killer Walter Resden to abusive Internal Affairs Agent Rick Stetler to corrupt judge Joseph Ratner. Some he thought put away for good come back to haunt him. Clavo Cruz, serving a life sentence for murdering a woman (episode 201, "Blood Brothers," episode 315, "Identity"), escapes custody in a dramatic rocket attack on a courthouse (superficially injuring coroner Alexx Woods). Cruz then kidnaps a court stenographer and forces Horatio to bring him $1 million dollars in exchange for her location. It is all a set-up, however, and Caine and Delko are ambushed on the roof of a parking garage. Though Horatio shoots down one man and escapes without injury, Delko is critically wounded even as Caine fires at the fleeing gunmen (episode 514, "No Man's Land"). Horatio eventually forces Cruz out of hiding by removing all his avenues of escape. Cruz approaches Horatio outside the Miami-Dade Crime Lab, and Caine kills Clavo with a single shot to the chest (episode 515, "Man Down").
Caine finds himself targeted by the son of Argento, a crime lord whom he helped put in jail some years earlier. After Caine's vehicle is vandalized, the young man smugly denies culpability. Horatio walks headlong into a trap and is shot at by the son. However, the rounds from his gun were replaced with blanks, Caine leaves without injury and the son is arrested afterward (episode 602, "Cyber-lebrity").
In the episode "Bone Voyage", when Raymond Langston comes to help Horatio and his team, he mentions about deceased CSI Warrick Brown, and asks Langston to tell Catherine Willows that he is sorry for their loss.
In the end of the Season 8 finale, he receives a shocking message from the man he arrested. The message said: "THEY ALL FALL DOWN". In the Season 9 premiere, he rushes to the crime lab, fearing for the team's lives. When he got out of the elevator, he finds everyone down and Eric still awake. Eric then tells him to shoot the window for oxygen. After Horatio does so, everyone gets up, except for Jesse Cardoza, who died during his fall. Horatio then tries to comfort the devastated Natalia Boa Vista, who unsuccessfully attempted to revive him. Horatio then joins the team on a game of basketball, in honor of Jesse at the end of the episode after they find the killer.
In "See No Evil" a large prison break occurs and one of the inmates (Joe LeBrock) states that they were planning on targeting Caine.
In the episode "Manhunt", he and the team track down Memmo Fierro, the man who was serving time for killing Marisol (Horatio's wife and Eric's sister) after he is one of the eight people who broke out in the previous episode. Memmo (under orders of Antonio Riaz of the Mala Noche) had shot Marisol then blocked the ambulance, trying to get Caine to come out, forcing the ambulance to drive over a center median (at the hospital, a doctor states that the car was worse than the bullet). Both the shooting and the blocking proved fatal to Marisol. At the end of the episode, Memmo takes a hostage, his daughter's social worker. Eric has a clear shot of him, but Horatio tells him not to shoot him in front of Memmo's daughter. After Memmo sees his daughter, he leaves with the hostage, who is later found dead.
In "Happy Birthday" Horatio is seen driving at the beginning of the episode with a bouquet of flowers on the passenger seat and leaves Eric a message on his phone asking him to take over for him a while so he can run an errand. He is distracted by a pedestrian who informs him a pregnant women has been assaulted on the side of the road. Leaving his errand behind, he helps the women and spends the rest of the episode looking for the people who did this to her while the mother and the baby are fighting for their life back in the hospital. At the end the episode the mother gives birth to a baby girl and we see Horatio at Marisols' grave and tells her the baby is "beautiful just like you". He then wishes her happy birthday.
In "Last Stand", Memmo returns with a gang of drug cartels, and Caine lays a trap for him, alone. Caine kicks Memmo multiple times and holds him at gunpoint. Memmo states him killing his wife was not personal, but Caine responds it was to him. Memmo asks if what Caine is doing is "righteous" and if he is at peace with his decision. Caine responds he is, and places him under arrest, and waits for backup to arrive.
In "Mayday", Horatio and Frank end up being held at gunpoint on a plane they were using to transport a fugitive. The plane crash lands, but the fugitive escapes. At the end of the episode, Horatio's fate is unknown as he has been shot by Randy Northe. Northe also temporarily stuns Natalia Boa Vista and drags her to a car where he stuffs her in the trunk. After speaking a few words to Natalia, he shuts the trunk door, turns the car on, and forces it to roll over the pier. Meanwhile, Horatio gains the ability to shoot at Randy, but is unable to save Natalia due to the gunshot Horatio received to his abdomen, It's likely that if Natalia hadn't stopped to help Horatio when he got shot, she may have been able to shoot Randy Northe, who had tricked them into walking straight into his trap.
In "Countermeasures" Horatio begins to have hallucinations of Marisol, saying she is glad to see him but he needs to go back. He is then shown back at the dock where he was shot, managing to get himself back up to his feet. Still bleeding from his gunshot wound, he jumps into the water to save Natalia, managing to free her from the car. As they are rushed to the hospital, he repeatedly calls Marisol's name. Against doctor's advice & still visibly in pain, he leaves the hospital to work on the case. He & the team manage to find North & try to get him to tell them where Toller is. Despite setting him up. Toller slips through his fingers once at a rail yard, but Walter discovers that the chemicals in the soot from Toller's old clothes could only have come from trash burned at a particular landfill. Horatio manages to find & capture Toller there after he very nearly sets another woman on fire. After leading Toller back to jail,Horatio finally concedes that he is not all right and agrees to get checked out.
In Long Gone Horatio is at it again with his vigilante like ways as he & Frank are escorting a suspect and Horatio assaults him for information, In Crowned Horatio & Natalia rescue a little girl from a rapist and Horatio chases him, the rapist shoots at Horatio & misses, then the rapist falls & is hanging over the ledge at a theater and instead of saving him Horatio just lets him fall to his death.
Battle vs. Keigo Kurusu (by SPARTAN 119)Edit
Keigo Kurusu walked into the Miami Airport terminal, having traveled there to hunt down a rival contestant in the battle royale for the right to become the next god of space and time. It would be difficult, as the contestant was not a criminal, meaning that his future diary was useless.
Meanwhile, Horatio also entered the terminal, having heard a police officer from Japan who had gone rogue had arrived, and was planning to commit a murder. Keigo walked out of the gate for a flight arriving from Sakurami International Airport, to be confronted by Lieutenant Horatio Caine, who was flashing a police badge at him.
"Keigo Kurusu", Caine said, "I would like you to come back to station with me and answer a few questions".
Keigo drew his Sig Sauer P226 and fired several shots, at Caine, who rolled out of the way just in time as bystanders fled around them. One of the rounds, however, flew into the window an airport security station, killing a guard. Keigo ran down the jetway and exited a side door, climbing down a ladder and running across the runway.
Keigo took cover behind a luggage cart and opened an item in his carry-on luggage, an M24 sniper rifle he had smuggled on board the aircraft along with his sidearm. Keigo fired a shot that grazed Horatio's side. Horatio jumped into the guard office next to the dead security guard and grabbed a Remington 700 sniper rifle in the gunrack. Lt. Caine rested the bipod of the sniper rifle on the edge of the window separating the security station from the main terminal and took aim, catching sight of the glint from Keigo's scope.
Horatio fired, the round flying across the tarmac towards Keigo. The round impacted Keigo's side, in the pocket he kept his future diary in. Suddenly, Keigo's body literally exploded in a swirl of color, just as a silver Humvee with the Miami-Dade PD logo drove in.
"What?!", Horatio thought, as he drew his Beretta Cougar and climbed down to meet the rest of the CSI team, who were now standing next to where Keigo disappeared, leaving only his rifle and a cell phone with a bullet hole through it.
"What happened?", Erik Delko, one of the members of the CSI team asked, "It looked like the perp imploded or something when you shot him."
"I don't know", Horatio said, "But I'd guess he couldn't live without his phone."
At that, Horatio took his sunglasses out of his pocket and put them back on.
YEAAAAA' *Insert "The Who- We Don't Get Fooled Again" here*
This was a close match up with very similar weapons and characters, but in the end, Horatio won this match over Keigo due to his slightly greater training and marksmanship. The "I guess he couldn't live without his phone" is a reference to a CSI Miami reference in Mirai NIkki Abridged at 4:30. (Yo dawg I heard you like references, so I put a reference in your reference)