Ercole DiMeo, a.k.a. "Old Man" and Ercole "Eckley" DiMeo, is the founder and the longtime Boss of the DiMeo crime family. By the events of the series, he is Boss in name only, and never demonstrated any influence over the family: he is serving a life sentence in a high security United States Prison in Springfield, Missouri. In season two, when Philip "Philly Spoons" Parisi picks up Gigi Cestone at the airport, we got some information about the prison where he is serving his life sentence. It is implied from the conversations that DiMeo is suffering from extreme old age and requires round-the-clock nursing care in the prison hospital wing. When the death of Giacomo "Jackie" Aprile is reported on television in season one, the newsreporter states that; he was the Acting boss for the 74-year-old Ercoli "Eckley" DiMeo, which then makes him over 80 years old at the end of the series.
DiMeo ran the family from sometime in the late 1950s or early 1960s until he received a sentence of life imprisonment in 1995, at which point Giacomo "Jackie" Aprile became Acting boss of the family. Though Jackie already had full control in 1999 (the first season of The Sopranos), at one point he said "I may be Acting boss while the old man's a guest of the government" out of deference to DiMeo.
DiMeo was apparently a major force in his prime. He served as a mentor to Tony Soprano and, according to other characters, had Tony and Jackie pegged early on as an eventual candidate for boss. DiMeo also took a liking to Tony's father "Johnny Boy" Soprano and it is likely that Johnny would have been Acting Boss had he not died of emphysema in 1986. However, it is clear that DiMeo had great muscle behind him when he led the family, as prominent capos "Johnny Boy" Soprano, Corrado "Junior" Soprano, and Michele "Feech" La Manna were below him.
DiMeo is based on the real boss of the North Jersey-based DeCavalcante crime family, Giovanni "John the Eagle" Riggi, an aging mobster serving a long prison term who made only the occasional intervention via the various acting bosses. The DiMeo/Soprano crime family is based on the DeCavalcante crime family.