Vladmir Lenin, the founder of Russian communism, was poisoned to death by his political successor Joseph Stalin, a sensational new theory has claimed.
Russian historian Lev Lurie, believes that while Lenin was already in poor health having suffered several strokes, Stalin may have finished him off after a bitter feud.
Lenin, who had initially supported Stalin's rise to power, later began aligning himself with Leon Trotsky.
In notes dictated before his death, Lenin criticises Stalin's rude manners and ambitious nature. He even suggested that Stalin should be removed from his position of General Secretary of the Communist Party, the Daily Mail reported.
Poisoning would later become Stalin's preferred method for dealing with his enemies, Lurie points out.
"The funny thing is that the brain of Lenin still is preserved in Moscow, so we can investigate," he added.
Popular theory maintains that Lenin died from the sexually-transmitted disease syphilis. His embalmed body still lies on public display in a Red Square mausoleum almost 20 years after the collapse of the communist state he helped bring to life.
Lurie and UCLA neurologist Dr Harry Vinters reviewed Lenin's records for an annual conference at the University of Maryland School of Medicine on famous people's deaths.
Dr Vinters put forward a separate theory, maintaining that stress or a family medical history could have accounted for Lenin's death. The 53-year-old Soviet leader's health had been growing worse over time. In 1921, he forgot the words of a major speech and he had to learn to speak again and write with his left hand after one stroke.
A subsequent major stroke later left him paralysed on one side and unable to speak.
Mr Vinters, who reviewed autopsy records and the leader's clinical history, said toxicology tests that might have revealed poisoning were not conducted during the autopsy.
Reports from the time also show Lenin was active and talking a few hours before his death.
"And then he experienced a series of really, really bad convulsions which is quite unusual for someone who has a stroke," Mr Vinters said.
The conference is held yearly at the school, where researchers in the past have re-examined the diagnoses of figures including King Tut, Christopher Columbus, Simon Bolivar and Abraham Lincoln.