Head of the Crime Lab
In the CSI continuum, Caine is (and has been throughout the show's
development) a supervisor at the Miami-Dade crime lab, a forensic analyst and former homicide detective and bomb squad officer (his forensic speciality is arson and explosion evidence). He is very protective of his team, who affectionately call him
"H." He is very concerned about the reputation of his lab, and takes great care to keep them clean, perhaps because of his
experience with his tarnished younger brother, Ray. Unlike his counterpart in Las Vegas, Gil Grissom (CSI: Crime Scene
Investigation), he does not hesitate to carry or use a weapon. In the first two seasons, Caine carried
a 9MM 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. One of Caine's reasons for selecting
Officer Ryan Wolfe as Speedle's replacement (in episode 302) is Wolfe's compulsive care of his firearm.
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"). 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: New York. 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").
He has many recurring enemies throughout the series, from serial killer Walter Resden to abusive Internal Affairs Agent Rick Stetler to the corrupt judge Joseph
Ratner (Resden and Ratner have since been arrested). 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").
Life Before CSI
Caine's parents named him for author Horatio Alger (CSI: Crime Scene
Investigation episode 222, "Cross Jurisdictions"). Before he moved to Miami, Caine worked in New York City before joining the Miami-Dade Police. (Coincidentally,
Caruso starred in the first two seasons of NYPD Blue as Detective John Kelly.) It was there that he killed the man who murdered his mother — his own father (episode
417, "Collision"). On the job, he was badly 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 (episode
406, "Under Suspicion"). Caine is eventually forced to shoot Resden (episode 415, "Skeletons").
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,
who is later tragically killed after accidentally triggering a bomb he is attempting to disarm (episode 102, "Losing Face").
Finally, Caine moves 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 goes on personal leave following the death of her
husband, Horatio becomes the permanent head of the lab (episode 1.01, "Golden Parachute").
 Personal life
Caine's original backstory, revealed over the course of the first
three seasons, revolves primarily around his relationship with his late brother Raymond Caine, also a police officer, and with Raymond's supposed widow, Detective Yelina Salas.
It was revealed in episode 320 ("Killer Date") that Raymond's apparent death had actually been staged to enable him to go
deep undercover to gather information for a government investigation. Raymond and Horatio are briefly reunited when Ray Jr.
is kidnapped. The brothers successfully rescue the boy and fake Ray Sr.'s death again before packing the whole family off
to Brazil (episode 324, "10-7"). Unfortunately,
Ray Sr. is unable to keep out of trouble even there, culminating in his murder; he dies in Horatio's arms (episode 501, "Rio").
The show also explores another of Caine's history: the events surrounding
his mother's murder. In the episode "Manhattan Manhunt", a
continuation of "Felony Flight", Caine is momentarily interrupted on his case when he is served with a subpoena. In "Nailed", Caine informs the rest of the CSI team that he had recently been
charged by a district attorney in New York with the murder
of the man who killed his mother. It is later revealed in "Collision" that this man was actually Caine's own father. After
arresting Resden, who is charged with murdering his foster siblings because they didn't defend against his abusive foster
father, whom he also attempted to kill, Caine reveals that he identifies with Resden because he, Caine, was physically abused
by his father.
After Speedle's death, Caine has a recurring nightmare in which he (Caine) is the one whose weapon misfired.
Rather than talking with a counselor, as Internal Affairs officer Rick Stetler orders, he instead works it out with his girlfriend, State Attorney Rebecca Nevins
(episode 310, "After the Fall".) He breaks up with her, however, after she makes a deal with a criminal he helped arrest (episode
313, "Cop Killer"). He later dates Rachel Turner, who is murdered by Walter Dresden in an attempt to take revenge on Caine
for "embarrassing" him in New York about a decade earlier
(episode 406, "Under Suspicion"). Caine also has a deep, unspoken affection for his brother's widow, Yelina Salas, and he
is consistently concerned about her well-being. Though she evidently shares his feelings, neither of them has acted on them
(episode 522, "Burned," et al.).
Caine was briefly married to Eric Delko's sister Marisol, who was shot by a Mala Noche gang member and later died (episode 424,
"Rampage"). He pursued the man who ordered the hit on her, Antonio Riaz, all the way to Rio de Janeiro in Brazil, and eventually killed him in hand-to-hand
combat after Riaz brutally beat Caine's brother Raymond to death and attempted to corrupt
Ray's son, Ray Jr. (episode 501, "Rio"). As Eric Delko lays in critical condition in the hospital following a near-fatal gunshot
to the head several months later, Horatio and the other team members take turns at his bedside. Delko, his memory impaired
by his wound, asks Horatio where Marisol is. Caine, nearly in tears, is unable to say the words, but Eric interprets his silence
and sheds wordless tears as they both mourn her death anew (episode 515, "Man Down").
He is very protective of crime victims, often going so far as to
give them his phone number should they need to talk. He remains very close to a lot of victims of crimes that he investigated,
and some from cases he worked in New York have actually followed him to Miami. He is very sensitive to the plight of children,
and reserves a special wrath for those who would hurt them, even against opposition from outside sources (CSI: Crime Scene
Investigation episode 222, "Cross Jurisdictions," CSI: Miami episode 503, "Death Pool 100", episode
407, "Felony Flight," episode 417, "Collision," et al.).
Perhaps because he has lost several family members to violent
crime, Caine is determined to the point of obsession to put criminals behind bars. Caine also advocates the death penalty,
and is not afraid to threaten suspects with it (CSI: NY episode 207, "Manhattan Manhunt").
He often seen putting on a pair of Silhouette Titanium Model
8568 sunglasses (with special polarized lenses). The online fans have started referring to the sunglasses as "The Sunglasses
of Justice" or "Justice Shades". Another interesting quirk about Caine is that he often stands sideways to the person to whom
he is speaking. He also has a habit of frequently smiling flirtatiously at his primary suspect. He is known for referring
to his colleagues by name and making vague statements suggesting that he knows more than he lets on.