Speculation about Lucan is on a level with that in the United States over labor leader Jimmy Hoffa, who vanished the following year.
Both were well-known personalities. Both disappeared suddenly, without a trace. And in each case, the lack of a confirmed sighting in the decades since led to endless theorizing over what really happened.
But more than 41 years after Lucan vanished, British courts have closed the book on the matter. On Wednesday, a London High Court declared Lucan dead, clearing the way for his son, George Bingham, to become the 8th Earl of Lucan.
The 7th Earl of Lucan -- whose name at birth was Richard John Bingham -- vanished November 8, 1974. He was a gambler, a man with expensive tastes, and one handsome enough to have once been considered for the part of James Bond.
At the time of his disappearance, he was separated from his wife, the former Veronica Duncan, and battling with her for custody of their three children.
Police believe he went to the family home in London's expensive Belgravia neighborhood on the evening of November 7. And there, authorities believe, he bludgeoned Sandra Rivett, the nanny, to death after having mistaken her for his estranged wife.
Lady Lucan was attacked as well, and she told authorities the assailant was her estranged husband.
Lord Lucan telephoned his mother and asked her to pick up the children. Then he drove to a friend's house. After that, he was never reliably sighted again.
A few days later, an arrest warrant was issued. But the trail had gone cold.
A slew of books on the case
Because Lucan was never found, stories and myths grew up around his disappearance. Hundreds of theoretical sightings of him were reported around the world. He was rich, he was poor, he was here, he was there, and so forth.
He was seen in France -- no, Colombia. Or India. Or New Zealand, where some people believed that a homeless ex-pat was really the missing lord.
Or maybe Gabon, on Africa's west coast, where, the story went, he watched from a distance as friends paraded his children by, unaware of their father's presence. Trouble is, his son denies ever having been to Gabon.
In the absence of hard facts, a slew of books was written, each claiming to have solved the mystery. They had titles such as "Lucan: Not Guilty," "Lucan Lives," "The Lucan Mystery" and "Lord Lucan: What Really Happened."
But now, legally at least, the case is closed. Lucan -- who, were he still alive, would be 81 -- is deemed to have died. His son, who had sought to have a court declare his father dead, is now free to become the 8th Earl of Lucan.
Though if the 7th Earl of Lucan really is dead, when, where and how he died, no one knows.
So the mystery remains.