Modi has reinvented himself from a controversial regional leader accused of turning a blind eye to religious riots in 2002 to an aspiring prime minister intent on helping India fulfill its potential. 

His promises to revive the economy have won him corporate cheerleaders, while his rags-to-riches story and reputation as a clean and efficient administrator satisfy many Indians' desire for strong leadership.

Attacks from his opponents — one called him a "devil" and the "Butcher of Gujarat" — as well as warnings from secular-minded critics and religious minorities have failed to dent his rise.

While Singh, 81, was hailed by US President Barack Obama as a "wise and decent man", Modi presents an awkward prospect for Washington and other Western powers.

The bachelor, elected three times as chief minister in his home state, was boycotted by the US and European powers over the 2002 Gujarat riots 
that left around 1,000 dead.

He denies that he turned a blind eye to the bloodshed and investigators have never found evidence of wrongdoing. 

David Cameron, the prime minister of former colonial ruler Britain, was among the first foreign leaders to congratulate Modi, saying he was "keen to work together to get the most from UK-India relationship".