Charles George Gordon was one of those eccentric individualists like Lawrence of Arabia who spring up in British history. He was a deeply religious man who spent most of his hard-earned salary (he often accepted *less* pay than he was offered) on charitable work. He helped the poor, educating destitute boys and providing pensions for the elderly. The grafitto 'God Bless the Kernel (Colonel)' was often seen scrawled on walls near his home.
He was also distrusted by the Establishment. A brilliant tactician and commander of troops he was constantly passed over for postings abroad because he was unpredictable. When he was asked to report on the grievances of the Basuto people by the British administration in South Africa, he sided with the Basuto and was shipped home very quickly. As Captain Willard says in 'Apocalypse Now': "They didn't dig what he had to tell them." You have to remember, too, that Gordon was a national hero. This was like firing Norman Schwarzkopf after the Gulf War.
The film fails to touch the depths of Gordon's character and in some cases is well off the mark (Charlton Heston seems far too interested in that Egyptian dancer!). We are shown that Gordon could be ruthless in the pursuit of justice (he executes a servant for theft, regardless of any personal feelings).
The fact remains that Gordon was a man of enormous moral and physical courage. He would not desert Khartoum and leave the people to be slaughtered. It now seems likely (and more in character) that he died fighting to the end.
The film is a tribute to that courage and some of the best moments occur when we are allowed to see the twinges of self-doubt and anxiety that Gordon suffered and overcame. The well-staged action scenes are like decoration on the moral diemmas at the heart of the film. Charlton Heston is physically wrong for the part but gives one of his best performances. He isn't outclassed by Olivier in any way, an achievement in itself.
