Daniel John Patrick Greene (November 14, 1933 – October 6, 1977) was an American mobster in Cleveland, Ohio, whose conflicts with the Cleveland crime family of the Italian-American Mafia ended in Greene's murder in 1977. Greene would build a close working relationship with Shondor Birns, as neither of them could become a "made" man in the Italian mob due to lack of Italian ancestry.

Greene first gained power in the local chapter of the International Longshoremen's Association (ILA), where he was elected president during the early 1960s. He later became a full-time crime boss and began competing with the Cleveland crime family, Jewish mob figure and one-time friend Shondor Birns for control of the city's criminal underworld. Greene set up his own crew called the Celtic Club, complete with enforcers and a close alliance with outlaw biker gangs. This club became the Irish mob, the Italian Mafia's main power competitor. This Celtic identity became Greene's trademark in the underworld.

During the 1970s, Greene allied with mob-affiliated labor union leader John Nardi during the latter's war against Jack Licavoli for leadership of the Cleveland family. The factions set more than 36 bombs, most attached to cars. While some of the bombs were unsuccessful in their attempts to harm, maim, or kill rivals, many victims were killed. 21 of the bombings were in the city of Cleveland and 16 of the bombings took place in the suburbs. It is estimated by the FBI that Greene was involved in three of every four bombings. Other bombings in Cleveland, like the Thinker statue at the Cleveland Museum of Art in 1970, Playhouse Square in 1970, and ones at Cleveland schools in the 1960s and 1970s by George Cicero, were unrelated to Greene and the Cleveland crime family.

After the humiliating failure of attempts on his life and Greene taunting the Licavoli faction as "maggots" in the local press, Greene was assassinated by Los Angeles crime family enforcers Ray Ferritto and Ronald "Ronnie The Crab" Carabbia.

A police investigation revealed that Greene's murder had been a criminal conspiracy between the Mafia families of Cleveland, New York City and Southern California. The investigation also resulted in the defections of Ray Ferritto and Los Angeles boss Jimmy Fratianno, followed by the exposure and arrest of a mole inside the Cleveland FBI. The investigation also laid the groundwork for many Federal prosecutions of the Mafia.

Daniel John Patrick "Danny" Greene was born November 14, 1933, in Cleveland, Ohio, to John Henry Greene and Irene Cecelia Greene (née Fallon). His father was also born in Cleveland, his mother was born in Pennsylvania.

Three days after his birth, Greene's mother died. He was called "Baby Greene" until his mother was buried, after which he was eventually named after his grandfather (Daniel John Greene). Danny's father drank heavily and eventually lost his job as a salesman for Fuller Brush. After this, Danny temporarily moved in with his grandfather (a newspaper printer), who had also been recently widowed. Unable to provide for Danny, his father placed him in Parmadale, a Roman Catholic orphanage in Parma, Ohio, three miles outside Cleveland.

In 1939, Danny's father began dating a nurse. He married her, and they started their own family and brought Danny to live with them.