Istanbul (AFP) - If there were a global contest for winning elections, Turkey's President Recep Tayyip Erdogan would see himself as the undisputed -- and undefeated -- heavyweight champion of the world.
In the 15 years since his ruling party came to power, Erdogan has taken part in 11 elections -- five legislative polls, two referenda, three local elections and a presidential vote -- and won them all.
On Sunday, Erdogan claimed victory in his 12t and arguably biggest ballot-box challenge since his ruling Justice and Development Party (AKP) came to power in 2002: a referendum on expanding his powers.
Supporters hail the new system as a historic change that will create efficient government but critics say it is a dangerous step towards one-man rule in the NATO member and EU candidate state.
Fighting for votes in every corner of the country, Erdogan kept up a punishing schedule of daily rallies seeking to woo doubters with his indefatigable campaigning.
Prowling around the stage like a rock star, a wireless microphone in his hand, Erdogan bellows at the crowds: "Do you want a strong Turkey?"
Known to his inner circle as "beyefendi" (sir) and to admirers as "reis" (the chief), Erdogan is supreme on stage, holding the audience with near-matchless public speaking skills.
- 'Balancing act' -
While Erdogan is widely seen in Western media as a near-omnipotent sultan, there are constraints to his rule, according to Asli Aydintasbas, senior fellow at the European Council on Foreign Relations.
To win Sunday's referendum, Erdogan had to perform a "delicate balancing act" of winning votes from both Kurds and nationalists, she added.
And the result was extremely tight with major cities Ankara and Istanbul voting against him.
Erdogan came to the referendum after the most turbulent year of his political life which saw a slew of terror attacks, worsening relations with Europe and above all a failed coup on July 15.
In a memorable image, he appeared on the FaceTime app on live TV to urge supporters to flood the streets and defeat the coup, saying he escaped being killed by just 15 minutes before returning in triumph to Istanbul.
The president has courted ever more controversy as authorities jailed more than 47,000 people under a state of emergency which has lasted nine months so far.
There has even been talk of fissures within the AKP and with his two other party co-founders -- former president Abdullah Gul and ex deputy prime minister Bulent Arinc -- both deafening in their silence by failing to endorse the new system.
- 'My crazy projects' -
With the new constitution likely to come into force after elections in November 2019, Erdogan could stay in power until 2029, by which time the energetic president, 63, would be 75.
He seems determined to leave a legacy at least as significant as Turkey's modern founder Mustafa Kemal Ataturk, whose picture hangs next to his at rallies.
He has embarked on a hugely ambitious drive to modernise Turkey's infrastructure with a new bridge and two tunnels spanning the Bosphorus, high-speed trains and the construction of a third airport for Istanbul -- schemes he affectionately refers to as "my crazy projects".
But critics worry of a creeping Islamisation of Turkey's officially secular society, with a surge in mosque-building, use of Islamic schools and the abolition of all restrictions on the headscarf in public life.
Born in Istanbul but brought up by the Black Sea, Erdogan is intensely proud of rising from humble origins to become Turkey's most powerful politician since Ataturk.
He gained prominence in the nascent Islamic political movements that were starting to challenge secular domination, becoming a popular mayor of Istanbul in 1994.
He was jailed for four months for inciting religious hatred when he recited an Islamist poem, a term which only magnified his profile.
Founding the AKP after the previous Islamic party led by his mentor Necmettin Erbakan was banned, Erdogan spearheaded its 2002 landslide election victory and became premier less than six months later.
It was in these early days that the AKP, lacking allies, forged an alliance with the movement of US-based preacher Fethullah Gulen that would end with the sides becoming sworn enemies and Gulen blamed for masterminding the coup bid.
- Return to pragmatism? -
Protests in 2013 over plans to build a shopping mall on an Istanbul park provided a rallying cause for secular Turks but Erdogan came out fighting, famously slamming the protesters as "capulcu" ("hooligans").
In 2014, Erdogan was elected president in the first-ever popular vote for the post and moved into a vast new presidential palace that opponents denounced as an extravagance.
In June 2015 elections, the AKP won the most votes but lost its overall majority for the first time. But Erdogan swatted away any proposal of a coalition and called new elections in November where the majority was restored.
Some analysts predicted the referendum result could soften the rhetoric of Erdogan, who enraged European leaders by frequently referring to "Nazis" after authorities cancelled 'Yes' camp rallies.
But the first signs suggested that yet another ballot box win had only emboldened the "chief", as he called on foreign powers to respect the result and mooted a referendum on restoring the death penalty -- which would sound the death knell for Turkey's EU bid.