Grady Alexander Rivers, the father of Celtics coach Doc Rivers, died peacefully in Chicago on Sunday, according to Celtics spokesman Jeff Twiss. The elder Rivers was 76 years old and arrangements for his funeral are expected to be made soon. Doc Rivers will miss today’s game against the Raptors in Toronto and is scheduled to fly from Canada to Chicago this afternoon. Celtics assistant Armond Hill and associate head coach Tom Thibodeau will coach in Rivers’ place. Hill has previous head coaching experience at Columbia University. Thibodeau has previous head coaching experience at Salem State.