Former Bruins defenseman Bobby Orr, who’s considered by many — us included! — to be among the two or three greatest hockey players ever to put on skates, is writing a book. Number 4’s ‘‘Orr: My Story’’ will be released in October by G.P. Putnam’s Sons, the publisher announced Tuesday. The two-time Stanley Cup champion (and three-time Hart Trophy winner as the NHL’s most valuable player) is promising to share experiences that are ‘‘worth putting down on paper.’’ According to the publisher, Orr will reflect not only on his phenomenal career but also his angry break with onetime friend and agent Alan Eagleson, who was jailed for fraud. The 64-year-old Orr, who’s now an agent and the owner of The Orr Hockey Group, was elected to the Hockey Hall of Fame in 1979. Wednesday, he’ll be downtown at the W Hotel, where his friend and former Bruins teammate Derek Sanderson will talk about the upcoming movie based on his life. Called “Turk,’’ the film is being directed by Doug Atchisonand will star Edward Burns as Sanderson’s father.