Ban's high profile and clean image were expected to be assets as he returned to a nation reeling from the corruption scandal surrounding President Park Geun-hye who has been impeached by parliament and stripped of her powers while a court decides her fate.
Ban said he did not want to run for the presidential position in South Korea as he was "disappointed at the selfish ways" of some of the politicians of the country and also complained of "fake news".
Former U.N. Secretary-General Ban Ki-moon said Wednesday that he won't run for South Korea's presidency, a surprise announcement that removes a well-known figure from contention and further stirs the country's already tumultuous politics.
"I, my family and the United Nations have been greatly hurt ..."
"I have made a decision to abandon my pure ambition of bringing about a change in politics, and uniting the nation", Mr Ban said.
South Korean presidential elections are scheduled for December, but if Park is removed from office, elections must be held within 60 days of the final ruling, the Post reported.
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It follows his less than successful return to Seoul last month, marred by a series of perceived PR gaffes and a scandal involving family members.
Even without saying he was running, his ratings in opinion polls had slipped to second place behind the presidential candidate for the main opposition Democratic Party, Mr Moon Jae In, after peaking at almost 30 per cent a year ago.
Ban's public profile was also affected when his brother Ban Ki-sang was indicted and a nephew was arrested in the USA in a bribery scheme involving a Vietnamese development project.
There had been little to propel Mr Ban's chances for the presidency in the absence of a political base and the lack of a clear message after his return from New York, Prof Kim said. "While his support ratings did not rise. he kept making mistakes".
The United States has indicted Ban's younger brother and his nephew on charges of bribery related to the sale of a high-rise building in Vietnam, and it has asked South Korea to extradite them both.