Colonel Callan was a mercenary soldier during the Angolan civil war of
1974-
1976. He was neither a colonel nor called 'Callan'; his real name was Costas Georgiou, he was of mixed Cypriot-British descent, and he was originally a private in the British Army's First Parachute Regiment. He was dishonourably discharged in the early 1970s due to his role in a robbery on a post office in
Northern Ireland, after which he moved to Africa and took to paid soldiering - an expanding industry at the time, due to a rash of civil wars in the newly-liberated colonies.
His chosen battlefield was Angola, where he was recruited by the Western-backed FNLA (the 'Front for the National Liberation of Angola', who were dedicated to the liberation of Angola from the MPLA, the 'Popular Movement for the Liberation of Angola', who were in turn dedicated to the liberation of Angola from UNITA, the 'National Union for the Total Independence of Angola', who were, in weary turn, dedicated to the liberation of Angola from both the MPLA and the FNLA).
Callan built up quite a legend around himself, as he proved to be an unstable psychopath, militarily inexperienced, but making up for it by ruthlessly executing prisoners and suspected deserters, and leading his men in frontal assaults against MPLA and UNITA forces, sustaining great casualties but caring not a jot. In an insane war, he slotted in perfectly, until, in 1975, he was wounded and captured by Cuban troops. Cubans were involved, I haven't mentioned them yet. Along with three other mercenaries, he was tortured and put to death. His body was flown back to Britain where, supposedly, baggage handers at the airport refused to unload it.
By the 1970s cowboys, spies, superheroes and private detectives were old-fashioned, and mercenary soldiers were the new heroes; with constant defence cuts and an efficient modern army, Britain in particular was a leading source of these dashing privateers, many of whom were blundering amateurs lured by tales of money and cheap glory, many of whom ended up dead or maimed with nothing to show for it. Callan's life and death highlighted this and led to paid soldiering becoming more shadowy and, supposedly, more professional during the 1980s; the romance had gone, its passing marked only by The Wild Geese and Elvis Costello's 'Oliver's Army'.