Widely seen as the only politician who could defeat Turkey's authoritarian President Recep Tayyip Erdogan at the ballot box, Imamoglu, 53, was catapulted into the headlines this week after his dawn arrest in a graft and "terror" probe.

In just four days, he went from being Istanbul's popular mayor to being arrested, interrogated then jailed on the day the main opposition CHP held a primary to name him their candidate for the 2028 presidential race.

After a sensational entry into politics in 2019 when he was elected mayor of Turkey's economic powerhouse, Imamoglu quickly became a key figure within the CHP.

But since then, his career has been overshadowed by a string of what critics say are politically motivated legal cases designed to cripple his plans to run for Turkey's top job.

After his arrest, Imamoglu vowed to fight on and "erase this black stain on our democracy" while the CHP branded it "an attempted coup".

The party urged people to hit the streets, which they did in their hundreds of thousands in at least 55 of Turkey's 81 provinces, defying threats from Erdogan and a protest ban.

"This is an incredibly important popular movement in terms of world political history as well as Turkey's political history," said CHP leader Ozgur Ozel.

"Ekrem Imamoglu is currently on his way to prison. But he is also on his way to the presidency."

- 'We will overcome' -

"This is nothing short of a coup against the main opposition party, with far-reaching consequences for Turkey's political trajectory," said Berk Esen, a political scientist at Istanbul's Sabanci University.

Hours before his arrest, Istanbul University revoked his degree -- a high-stakes move as presidential candidates must have a higher education diploma.

Although he was seen as best placed to challenge Erdogan in the 2023 race, Imamoglu did not run due to an unresolved defamation conviction.

Since then, his legal woes have multiplied with three new probes targeting him this year alone.

His resounding re-election as mayor last year despite Erdogan's best efforts to unseat him has cemented the popularity of the football-loving father-of-three.

Born in Akcaabat on the northeastern Black Sea coast, Imamoglu moved to Istanbul as a teenager.

After studying business, he graduated in 1995 then went to work in the construction industry.

He was a political unknown until 2010 when he managed to end the 25-year dominance of Erdogan's AKP and its allies in Istanbul where the president also once served as mayor.

As Erdogan's own career path has shown, running the megalopolis of 16 million is a tried-and-tested route to national power.

Initially stripped of victory when the vote was annulled, he won by an even bigger margin in a re-run three months later, telling his ecstatic supporters they had "opened the door to a new future".

But the legal cases against him quickly began stacking up: in 2022, he was convicted of defamation for a throwaway remark calling Istanbul election officials "idiots".

Sentenced to 31 months in prison, he appealed but the outcome remains pending, with CHP deciding not to field him in the 2023 presidential race given the jail threat.

In 2023, prosecutors named him in a graft probe for alleged tender-rigging while mayor of the Istanbul district of Beylikduzu -- one of the grounds for his arrest on March 19.

In January, prosecutors opened two more probes over his remarks about Istanbul's chief prosecutor and a court-appointed expert witness.

- 'Breath of fresh air' -

A practising Muslim in a secular party, the smooth-talking politician has won support from a wide spectrum of voters.

"Imamoglu is the only kind of Turkish politician who can defeat Erdogan," said Soner Captagay of the Washington Institute for Near East Policy.

He had qualities that resembled Erdogan -- being savvy in business and life, both pious and a nationalist, he said.

"But unlike Erdogan, he is also a social democrat with a base of right-wing, left-wing and centrist voters, in contrast to Erdogan's base of right-wing voters only," he said.

"On top of it, he's 20 years younger and many voters, even those who like Erdogan, see him as a politician who would bring a breath of fresh air to Turkish politics."

Esen agreed, saying his appeal lay in the fact he could "attract all segments of the opposition electorate, whether Turkish or Kurdish, Sunni or Alevi, young or old," he said.