Trump wallowed in political incorrectness as he insulted everyone from Mexican immigrants to Jeb Bush and US ally
"I will be the greatest jobs president that God ever created," Trump predicted in a long, combative speech in the atrium of Trump Tower on Manhattan's Fifth Avenue.
The billionaire, widely seen as having almost no chance of winning the nomination, brings an outsized personality and a penchant for controversy to an unusually large group of Republicans vying for the presidency.
Trump, who owns several hotels and hosts the reality show "The Celebrity Apprentice" on NBC, boasted having US$8.7 billion in net worth, a number he says he released so that America understands he is not a loser.
Trump has flirted with the notion of running in past elections, but has ultimately backed out each time. This time, he said, the United States needs him to come to the rescue and revive a “dead” American dream.