Al Giardello – nicknamed "Gee" after the only thing he could say when called to his first murder scene as a rookie as well as a reference to his last name – is the commander of the homicide unit shift followed by the series.

As Bayliss tries (and fails) to hustle him out of some easy cash during a slow night, he learns from Munch that Gee put one of his three children through college by playing Hearts for money.

In the Season 6 episode "Lies and Other Truths", it is revealed that Gee has kept in touch with a former KGB agent who apparently held him captive at some earlier point in his life.

A physically imposing, highly articulate man, Giardello's cultural attitude stands in sharp contrast to both his Baltimore upbringing and many other officers in the Department.

In Season 4, Gee delays his flight out of Baltimore for a daughter's wedding for so long that by the time he does get to BWI, the weather has made it impossible for him to fly to the event in San Francisco, and he is left devastated.

One of the victims is Gee's cousin Mario, whom Mike remembers fondly from his childhood and who was killed as a result of his decision to testify against a union boss 25 years earlier.

When someone under his command gets too far out of line, though, he can take them to task very sharply, at one point even forcing Bayliss to apologize to "the bosses" for making an angry phone call to them over a case.

Giardello tends to allow his detectives to investigate murders in a manner that is more efficient but less discreet, very much unlike the preferred methods instructed by the department's upper command.

Gee's leadership style and earned respect from his detectives mirrored the real-life dynamic with Lt. Gary D'Addario, who had a recurring role on the show as SWAT team commander Lt. Jasper.

Early in the series, Giardello finds conflict with George Barnfather, a college-educated bureaucrat who is less experienced on the street and more interested in appeasing those who outrank him.

Giardello is particularly incensed when Barnfather refuses to grant Steve Crosetti an honor guard because his suicide would create bad publicity for the department.

Harris had asked Detective Frank Pembleton to cover up a scandal involving congressman Jeremy Wade, which nonetheless resulted in a lost election.

Giardello joined the BPD in 1968 during a racially turbulent era and was subject to working under a predominantly White department in a largely African American city.

Within the BPD, Gee is repeatedly passed over for promotion to captain by African American commanders Deputy Commissioner James Harris and Colonel George Barnfather for White officers Megan Russert and Roger Gaffney, both of whom are less experienced and less competent.

In Homicide: The Movie, Gee has left the department and is running for mayor on a platform in favor of drug legalization, with a considerable lead in the polls.

Gee subsequently finds himself in an afterlife version of the homicide squad room, filled with the spirits of murder victims and police officers, and briefly meets Adena Watson before sitting down to play cards with Detectives Steve Crosetti and Beau Felton.