Who is Turkish opposition leader Ekrem Imamoglu?

Ekrem Imamoglu, the Turkish presidential hopeful arrested on corruption charges, remains one of the country's most popular politicians.

A leading figure in the opposition Republican People's Party (CHP) and mayor of Istanbul, the 54-year-old has long been seen as President Recep Tayyip Erdogan's most formidable rival.

He stunned Erdogan and his ruling Justice and Development Party (AK) when he retained control over Istanbul in last year's municipality elections, winning a second successive mandate in Turkey's largest city.

Many political commentators in Turkey have referred to this as "Erdogan's worst defeat ever".

Imamoglu's arrest, just days before the CHP's primary election when he was expected to be chosen as the 2028 presidential nominee, has thrown his candidacy into doubt.

Imamoglu was formally arrested and charged with corruption four days after his detention. It triggered the country's largest protest in years, and security forces responded with tear gas and rubber bullets.

He has said the allegations against him are politically motivated and criticised his arrest as a "black stain on our democracy".

Born in 1970 in Akcaabat, a seaside town in Trabzon province on Turkey's Black Sea coast, Imamoglu moved to Istanbul as a teenager, studied business and then went to work in the construction industry.

Despite his family's centre-right, conservative background, Imamoglu says he "embraced social democratic values during his time in university".

A football enthusiast, like Erdogan himself, Imamoglu was also an amateur player in his youth and is well known for his support of his local club, Trabzonspor. A love of the sport is a useful characteristic for a politician in football-mad Turkey.

After a business career, at the age of 43 he turned to politics and was elected mayor of Istanbul's middle-class Beylikduzu district for the CHP.

But he was still relatively little known until he fought and won mayoral elections in Istanbul in 2019, which came as a major shock to Erdogan and the AK.

Imamoglu faced immediate challenges to his victory - the electoral authorities annulled the vote and forced him out of office after the AK alleged irregularities in the voting process. A re-run was ordered.

After the announcement of the re-run, Imamoglu addressed huge crowds of his supporters at a rally, taking his jacket and tie off, rolling up his sleeves and urging them to focus their energy on winning again.

"Everything will be fine," he said, which became his campaign slogan and has been his catchphrase ever since.

And for Imamoglu, "everything did go fine" - he secured 54% of the votes in another huge blow to the president.

He had now beaten the AK twice, in a city which the governing party and its Islamist predecessors had run for 25 years.

Istanbul is where Erdogan grew up, selling sesame bread snacks before going into politics in the 1970s. It was here that he rose through the ranks to become mayor, prime minister and ultimately president.

This loss would have stung him personally and hurt his party too. Istanbul is home to a fifth of Turkey's population of nearly 85 million and responsible for a significant portion of its economy, including trade, tourism and finance.

Many experts predicted a similar rise to power for Imamoglu after he won a second mandate in 2024. For many, he was becoming a threat to Erdogan's grip on Turkey's top office.

Erdogan secured a third term in presidential elections in 2023 and under the constitution he cannot govern beyond 2028.

But his critics say he might change the constitution in order to seek yet another term. The next poll is scheduled for 2028, but likely to happen earlier.

During his political campaigns, Imamoglu has been praised for his soft, humorous approach to politics, which contrasts with that of many rivals in Turkey's polarised political landscape.

Broadening the CHP's secular base, he has managed to appeal to some of Turkey's more pious, conservative voters, who had traditionally voted for the AK, by including visits to mosques in his election campaigns and recently announcing the restoration of a historic mosque in Istanbul's popular Karakoy district.

His wife Dilek Imamoglu has also become a popular figure with her active presence on social media, involvement in charity work for the disabled and appearances alongside her husband during his campaign.

Imamoglu's Istanbul University degree was annulled the day before his arrest, due to alleged irregularities. Under the Turkish constitution, presidents must have completed higher education to hold office.

Despite this, the CHP pushed ahead with a symbolic presidential nominee vote on Sunday, with nearly 15 million people casting their vote in solidarity against Imamoglu's arrest, chairman Ozgur Ozel said. The BBC cannot independently verify this figure.