Robert De Niro stepped in to take over the role originally played by the late James Gandolfini. When scheduling issues forced De Niro to drop out, John Turturro took the role.
HBO originally passed on the pilot. HBO later picked up the series after James Gandolfini and Steven Zaillian agreed to make a mini-series instead of an open-ended series. Gandolfini died suddenly a month later.
"The Night Of" is based on a British TV series that ran from 2008-09 called "Criminal Justice." This can be confirmed by credit that is displayed after each episode.
It is a joint project between the BBC and HBO.