Ex-UKIP leader Nigel Farage has launched his new Brexit Party, saying he wants a "democratic revolution" in UK politics.
Speaking in Coventry, he said May's expected European elections were the party's "first step" but its "first task" was to "change politics".
"I said that if I did come back into the political fray it would be no more Mr Nice Guy and I mean it," he said.
But UKIP dismissed the Brexit Party as a "vehicle" for Mr Farage.
The launch comes after Prime Minister Theresa May agreed a Brexit delay to 31 October with the EU, with the option of leaving earlier if her withdrawal agreement is approved by Parliament.
This means the UK is likely to have to hold European Parliament elections on 23 May.
Mr Farage said the Brexit Party had an "impressive list" of 70 candidates for the elections. Among those revealed at the launch was Annunziata Rees-Mogg, sister of leading Conservative Brexiteer MP Jacob Rees-Mogg.
Mr Farage said: "This party is not here just to fight the European elections... this party is not just to express our anger - 23 May is the first step of the Brexit Party. We will change politics for good."
He said he was "angry, but this is not a negative emotion, this is a positive emotion".
The party had already received £750,000 online over 10 days, he said, made up of small donations of up to £500.
Ms Rees-Mogg said she had stuck with the Conservatives "through thick and thin", but added: "We've got to rescue our democracy, we have got to show that the people of this country have a say in how we are run."
Who is Annunziata Rees-Mogg?
Annunziata Rees-Mogg joined the Conservative Party, at the age of five, in 1984. She says she canvassed for the party from the age of eight.
The sister of Conservative Brexiteer MP Jacob Rees-Mogg, Ms Rees-Mogg stood unsuccessfully as a Conservative candidate in the 2005 and 2010 general elections.
The freelance journalist has written for the Daily Telegraph, MoneyWeek and the European.
Earlier, Mr Farage told BBC Radio 4's Today programme: "In terms of policy, there's no difference (to UKIP), but in terms of personnel there is a vast difference.
"UKIP did struggle to get enough good people into it but unfortunately what it's chosen to do is allow the far right to join it and take it over and I'm afraid the brand is now tarnished."
He promised the Brexit Party would be "deeply intolerant of all intolerance" and would represent a cross-section of society.
UKIP leader Gerard Batten tweeted that Mr Farage's suggestion that there was no difference in policy between UKIP and the Brexit Party was "a lie".
He said: "UKIP has a manifesto and policies. Farage's party is just a vehicle for him."
He said the Brexit Party's "only purpose is to re-elect him (Mr Farage)" and was a "Tory/Establishment safety valve".
The Electoral Commission has issued European Parliamentary elections guidance for returning officers to advise them "on the rules should the elections go ahead" and to ensure they "have as much certainty as possible in developing contingency plans".