The compelling story of one of the most successful mountain gorillas that has ever lived - a huge silverback called Titus. The programme starts in 1967, when the researcher Dian Fossey first made contact with a group of mountain gorillas in Rwanda. She opened up a window on to their secret lives. Forty years on, this film reveals the complete and dramatic life story of one individual animal. Titus's father was murdered by poachers in front of his very eyes. His mother abandoned him in the subsequent chaos. His family disintegrated. He should have died. But we reveal how Titus survived against all the odds. Titus's present day trials and tribulations take the viewer back in time to reveal key moments in Titus's history. Using testament from eyewitnesses, the film relives one individual mountain gorilla's extraordinary battle for survival.

• Bernard Hill