Al Capone, the infamous mobster and convicted tax cheat, spent 4.5 years of his prison sentence at Alcatraz. Capone was transferred to "The Rock" in large part to cut off his communication with the outside world and his former mafia cohorts.

Related Fact:
Alcatraz got its name in 1775 after being referred to as La Isla de los Alcatraces (AKA Island of the Pelicans) by a Spanish naval officer named Juan Manuel de Ayala.

[Source: The History Channel. See previous Numbers of the Day here.]