Golgomath becomes Gurg of the Giants when he kills his predecessor, Karkus, and throws his head in a lake (OP20).
Karkus is killed two days after he was contacted by Hagrid and Madame Maxime in the summer of 1995 (OP20).
Golgomath kills and succeeds Karkus
Date summer, 1995
Certainty Stated in canon
Location in Canon OP20
Type of Event Wizarding world