Who is Bill Tanner from You Only Live Twice and what is their importance?

Bill Tanner is the Chief of Staff in the Service and Bond's best friend. Bond inquires as to why he has been placed in this mission and not a Japanese man. Tanner tells him that M thought Bond would be the best man for the position. Tanner suggests that Bond could be moved out of the Double-O section, to which Bond claims he will seek his old number upon his return. Bill Tanner gives details to Bond about his mission. He tells him that he will be working with Richard Lovelace Henderson, Dikko, as a go-between for information between Britain and Australia.