Broderick Bode was a sallow-skinned wizard with a mournful face who worked for the Department of Mysteries (GF7, OP8). He was injured late in 1995 when Lucius Malfoy Imperiused Bode into removing the Prophecy from the Department of Mysteries (OP26). Bode lost the power of speech and thought he was a teapot. He was regaining his health at St. Mungo’s (OP23) when he was assassinated by a Devil’s Snare plant that strangled him to death (OP19, OP23, OP25).
"To bode" = to portend or be an omen for something. It has a somewhat sinister connotation, although it can mean either good fortune or bad.
It's ironic that this 'Unspeakable' was rendered incapable of speech by his injuries.
Who killed him? While at St. Mungo's, he was visited by a "very old stooped wizard with a hearing trumpet" (OP22). And according to a (non-canon) planning chart for Order of the Phoenix (OP Plan), Macnair was the one visiting Bode at St. Mungo's on Christmas Eve.