Although he was boss only for about 14 years already in the 30s Joseph Francis Civello was a leader.

Joseph Francis Civello (February 3, 1902 – January 17, 1970) was an American mobster and the leader of the Dallas crime family from 1956 until his death in 1970.

Early life
A native of Baton Rouge, Louisiana, Civello had moved to Dallas as early as July 1928 when he was arrested for the murder of Joe DeCarlo at the St. Paul Drug Store in Dallas. Reportedly, DeCarlo's dying words were that the close-range shotgun blast to his abdomen was accidental. Based on this information, a grand jury did not issue an indictment against Civello.[1][full citation needed] Civello was an expert marksman and regularly participated in skeet shooting competitions as a longtime member of the Dallas Gun and Skeet Club.[2][full citation needed]

By the early 1930s, Civello had organized a crew (dubbed The Civello Gang by the Dallas Morning News)[3][full citation needed] which included cousins Sam Civello, Louis Civello, Leon Civello, Frank Ianni, and Joe Cascio, among others.[4][full citation needed] The gang operated as associates of Dallas' Piranio crime family, and was involved primarily with bootlegging and narcotics trafficking.

The Civello gang's main rival during this time was a Jewish gang headed by Nathan Biegler. In 1935, when Biegler was sentenced to 10 years in Leavenworth Federal Penitentiary, another Jewish gangster, Louis "Big Daddy" Ginsberg, came to Dallas from Chicago to reorganize the remnants of Biegler's gang. Both the Civello Gang and the Ginsberg Gang were heavily involved in the sale and distribution of morphine and heroin. The Civellos collaborated almost exclusively with associates of Charles "Lucky" Luciano of New York City, while the Ginsbergs' drugs came from mobsters in Chicago.

Merlino has been the boss of Philly since the mid 90s

How long did the old bosses rule for? The old mustache Pete’s so to speak before the five family formulation

If you believe the G that he's the boss. And according to the FBI he is, or was, he's had a pretty long run. He's had a tough run because he served a lot of time. But it is what it is I suppose.