Derrick Parker, a New York City police detective whose love of rap music and deep knowledge of the city’s music and celebrity scene made him the Police Department’s go-to expert for crimes involving entertainers like Sean Combs, Jennifer Lopez and Lil’ Kim, earning him the nickname “the Hip-Hop Cop,” died on July 24 in East Meadow, N.Y., on Long Island. He was 65.

His brother Strickland Parker confirmed the death, in a hospital, from a heart attack.

Born in Brooklyn and raised there and in Queens, Mr. Parker joined the Police Department in 1982, and his rapid ascent through the ranks paralleled the explosive growth of the hip-hop music scene in New York and elsewhere.

As that scene evolved, so, too, did its criminal element, culminating in the 1996 murder of Tupac Shakur and the 1997 murder of Christopher Wallace, known as the Notorious B.I.G.

Mr. Shakur was killed in Las Vegas and Mr. Wallace in Los Angeles, but both cases had ties to New York, where Mr. Parker, then a detective with the cold-case unit, played a key role in the investigations.

Both cases remain unresolved, though a trial in Mr. Shakur’s killing is now underway. But Mr. Parker’s connections and insights proved so valuable that the department reassigned him to a full-time job tracking the intersection between crime and the city’s hip-hop community.

“What interested me was, I saw a lot of these guys that were really bad dudes in Brooklyn starting to latch onto rappers and entertainers,” he told The Village Voice in 2004. “So I used to monitor the incidents, department-wide, of anything that happened.”

Before a rapper made a club or concert appearance, Mr. Parker would brief officers on the artist’s entourage and criminal background, and on possible safety threats. When a crime occurred involving a musician, he was called to the scene — even in the middle of the night.

In December 1999, he received a late-night call about a shooting at Club New York, in Midtown Manhattan, at which Mr. Combs and Ms. Lopez, his girlfriend at the time, were present. Three people were injured, one seriously. Mr. Combs, Ms. Lopez and two associates fled in a car, leading police on a chase through the city. They were eventually caught and arrested.

When Mr. Parker arrived at the Midtown North Precinct, he found Ms. Lopez handcuffed to a cell cage and a scrum of attorneys trying unsuccessfully to see her and Mr. Combs.

Consummately diplomatic, Mr. Parker arranged for the lawyers to enter and for Ms. Lopez’s release — and helped dissuade her from filing a lawsuit. Mr. Combs was acquitted on charges of weapons possession and bribery. One of his rap protégés, Shyne, was sentenced to 10 years for assault.

In 2001, Mr. Parker was called in after gunfire was exchanged one afternoon in Manhattan between the entourages of the rappers Lil’ Kim and Capone, a friend of Foxy Brown, who was feuding with Kim. One person was injured.

Once more, Mr. Parker acted as a liaison between the police and the various factions involved in the shooting. Lil’ Kim was sentenced to a year in prison for lying about who was involved in the incident.

A 6-foot-3, roughly 300-pound, gregarious man known to friends as Easy D, Mr. Parker was well known and well liked by his fellow officers and in the New York entertainment world. Even many of the people he arrested accorded him respect, long after he left the police force and started a company that ran security for nightclubs, concerts and wrestling events.

“D and I were working a door one night, and this guy sees D,” Glen Beck, Mr. Parker’s business partner and close friend, said in an interview. “He gives him a pound and a hug, and D gives him a comp. As soon as he walks by, D says: ‘He just got home from 15 years. I put him away.’”

While still with the department, he moonlighted as a security guard for the World Wrestling Federation (now World Wrestling Entertainment). He also worked as the promotional director for Chocolate Singles, a magazine for young single Black people, organizing parties and group vacations. In 1988, he even cut a record, “Single Man.”

Mr. Parker’s police role was controversial. His position at the department starting in 1999 was officially within its gang-intelligence unit, and he was tasked with keeping a database of personal details — an assignment that made him, in the eyes of some, a spy.

Mr. Parker didn’t see it that way. He felt that he was helping protect the artists he admired and the scene he loved.

“My goal was never just to arrest and convict rappers,” he told The New Yorker in 2008. “I wanted to let law enforcement know about rap’s inner workings, and show the majority, nonviolent element in rap that there were law-enforcement people on their side. My basic goal was to protect rap music from itself.”

Derrick James Parker was born on May 8, 1961. His father, Lionel, was a retired Marine Corps sergeant and a sanitation police officer. His mother, Dolores (Bryant) Parker, was the daughter of the vocalist and bandleader Willie Bryant (1908-64), whose conversational singing style earned him a reputation as a forefather of rap.

In 1979, Mr. Parker entered St. John’s University and studied public administration for three years before leaving to enroll at the police academy. He received a bachelor’s degree from John Jay College of Criminal Justice in 1984.

After a few years as a beat cop in Midtown Manhattan and as an undercover narcotics officer in the Bronx, Mr. Parker become one of the youngest detectives in the department.

For about a decade, he handled homicide cases in the Bedford-Stuyvesant neighborhood of Brooklyn, and in 1996 was chosen to join the department’s newly formed cold-case unit, where he worked until 1999.

He retired from the force in 2002, after which he went to work for Mr. Beck’s security company. The two later formed their own business as partners.

In 2006, he published a memoir, “Notorious C.O.P.: The Inside Story of the Tupac, Biggie and Jam Master Jay Investigations from the N.Y.P.D.’s First ‘Hip-Hop Cop,’” written with Matt Diehl.

Along with his brother Strickland, Mr. Parker is survived by three other brothers, Ralph, Tracy and Lionel Jr., and a sister, Tonea Parker.

Mr. Parker maintained his connections within the hip-hop world long after he left the Police Department, and Mr. Beck said that detectives and captains kept his number on speed dial in case they needed his advice.

“The street will tell you everything you need to know, if you wait patiently,” Mr. Parker told The New Yorker. “The street knows everything.”