The 57-year-old is a former Communist who has been a Labour Party member for the past 10 years.
He describes himself as a "lieutenant of the Left" who would not be offering Downing Street "blind allegiance".
He says that while he is not a Blairite, he is not anti-Blair.
Mr Simpson launched the campaign to oust Amicus leader Sir Ken Jackson.
'Dirty tricks?'
Sir Ken, the union leader closest to Mr Blair, is 65 this year and insisted that he wanted to stay on until 2004 to oversee the union's merger of the Amalgamated Engineering and Electrical Union with Manufacturing, Science and Finance.
Mr Simpson was forced to resign his union official role to stand against him.
He argued that he was a victim of a dirty tricks campaign, by being denied time off to attend the union's conference, having emails blocked and being disciplined.
He has no plans to threaten to cut funding to the Labour Party but argues that the UK has the worst labour laws in Europe.
He says he wants to see legislation introduced to look after the interests of workers, jobs and pensions.
Reunited
Mr Simpson left school in Sheffield at the age of 15 and took up an apprenticeship in a local engineering firm.
He quickly became involved in union work, attending the engineering union's youth conference.
He became a shop steward, then a convenor before being appointed the union's Sheffield district secretary in 1981.
He has an Open University degree in computing and mathematics.
The father-of-three has recently reunited with his wife after the couple divorced more than 20 years ago.
He is a keen chess player, enjoys listening to all types of music and spends a lot of time "messing about" with computers.