Answer by taking a quote from the following article:

Fred Hampton (August 30, 1948 - December 4, 1969) was an African-American activist and revolutionary, chairman of the Illinois chapter of the Black Panther Party (BPP), and deputy chairman of the national BPP. Hampton and fellow Black Panther Mark Clark were killed during a raid by a tactical unit of the Cook County, Illinois State's Attorney's Office, in conjunction with the Chicago Police Department and the Federal Bureau of Investigation in December 1969. In January 1970, a coroner's jury held an inquest and ruled the deaths of Hampton and Clark to be justifiable homicide. However, a civil lawsuit was later filed on behalf of the survivors and the relatives of Hampton and Clark.

About the same time that Hampton was successfully organizing young African-Americans for the NAACP, the Black Panther Party (BPP) started rising to national prominence. Hampton was quickly attracted to the Black Panthers' approach, which was based on a ten-point program that integrated black self-determination on the basis of Maoism. Hampton joined the Party and relocated to downtown Chicago, and in November 1968 he joined the Party's nascent Illinois chapter--founded by Student Nonviolent Coordinating Committee (SNCC) organizer Bob Brown in late 1967. Over the next year, Hampton and his associates made a number of significant achievements in Chicago. Perhaps his most important accomplishment was his brokering of a nonaggression pact between Chicago's most powerful street gangs. Emphasizing that racial and ethnic conflict between gangs would only keep its members entrenched in poverty, Hampton strove to forge a class-conscious, multi-racial alliance between the BPP, the Young Patriots Organization, and the Young Lords under the leadership of Jose Cha Cha Jimenez.  Fred Hampton met the Young Lords in the Chicago Lincoln Park Neighborhood, the day after the Young Lords were in the news after they had occupied a police community workshop meeting, held on the second floor hall of the Chicago 18th District Police Station. Later, the Rainbow Coalition was joined nationwide by the Students for a Democratic Society ("SDS"), the Brown Berets, and the Red Guard Party. In May 1969, Hampton called a press conference to announce that this "rainbow coalition" had formed. It was a phrase coined by Hampton and made popular over the years by Reverend Jesse Jackson, who eventually appropriated the name in forming his own, unrelated, coalition, Rainbow/PUSH.  Hampton's organizing skills, substantial oratorical gifts, and personal charisma allowed him to rise quickly in the Black Panthers. Once he became leader of the Chicago chapter, he organized weekly rallies, worked closely with the BPP's local People's Clinic, taught political education classes every morning at 6am, and launched a project for community supervision of the police. Hampton was also instrumental in the BPP's Free Breakfast Program. When Brown left the Party with Stokely Carmichael in the FBI-fomented SNCC/Panther split, Hampton assumed chairmanship of the Illinois state BPP, automatically making him a national BPP deputy chairman. As the Panther leadership across the country began to be decimated by the impact of the FBI's COINTELPRO, Hampton's prominence in the national hierarchy increased rapidly and dramatically. Eventually, Hampton was in line to be appointed to the Party's Central Committee's Chief of Staff. He would have achieved this position had it not been for his death on the morning of December 4, 1969.

What was his position in the Black Panthers?
Perhaps his most important accomplishment was his brokering of a nonaggression pact between Chicago's most powerful street gangs.