Peter Cruddas was principal treasurer of the Conservative Party for less than a month before he was forced to resign.
The former banker founded internet securities dealer CMC Markets in 1989.
He began with a £10,000 investment and built it into a global player, with partnerships in more than 30 countries.
CMC deals in areas such as spread betting, foreign exchange and gold and oil trading.
According to the company's website it deals with over 26 million trades each year. It has an estimated worth of £1.25 billion.
Mr Cruddas, who is 90th in The Sunday Times Rich List, has amassed a £750 million fortune. In 2006 he was described as the richest man in the City.
The Arsenal fan, who left school aged 15, has held positions in several charities, such as The Duke of Edinburgh's Award, The Prince's Trust and Great Ormond Street Hospital.
Cruddas also runs a charitable trust, the Peter Cruddas Foundation.
It says Mr Cruddas is "passionate about his charitable work with the Foundation and is also active in a numberof other charitable institutions, which the Foundation supports."