He stood as an independent and became the first mayor of London in May 2000 when then-prime minister Sir Tony created the powerful post.
In his second term, which he won as the official Labour candidate, he earned praise for the way he stood up for London after the July 2005 suicide bombings and helped win the 2012 Olympic Games for the capital.
Mr Livingstone lost City Hall in 2008 when he was defeated by an equally colourful opponent in Boris Johnson and a failed bid to return to office in 2012 marked the end of his electoral ambitions.
He became embroiled in a string of allegations of anti-Semitism, over which he quit the Labour Party in 2018.
It came after a long-running row over his claims that Adolf Hitler had backed Zionism in the 1930s, which had originally seen him suspended from the organisation in 2016.
The ex-Brent East MP was singled out in a human rights watchdog report in 2020 into how Labour dealt with anti-Semitism claims, which said Jewish Labour Party members felt he had made comments that “had the effect of stirring up and fuelling hatred for Jews”.
On Tuesday, it was reported that Mr Livingstone withdrew a legal challenge to the Equality and Human Rights Commission’s report.
The Alzheimer’s Society praised his family for “being open about his diagnosis”.
Chief executive Kate Lee said: “We are really sorry to hear that Ken Livingstone is living with Alzheimer’s disease. Our thoughts are with him and his family.
“We can see from the high profile individuals who have recently spoken about their dementia diagnosis, including Alastair Stewart and Fiona Phillips amongst others, how prevalent dementia is. One in three people born in the UK today will go on to develop this devastating condition.
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