A man from Luton, Bedfordshire, claims to have fathered 'in excess of 800 children' through unlicensed artificial sperm donations.
Simon Watson began by donating at sperm banks, but he has been offering unlicensed donations for 16 years.
Although unlicensed donation is legal, critics say the use of unregulated donors puts women at risk of sexually transmitted diseases and their children at risk of hereditary disorders.
Mr Watson, who at 41 has just passed the age range of eligible donors set out by guidelines from the HFEA, Human Fertilisation and Embryology Authority, finds most of his clients via Facebook. He offers his services for £50 (compared to £500 to £1000 at a private clinic).
'I give them a syringe with the pot, and then leave them to it,' he told the Victoria Derbyshire programme.
He estimates that he has fathered in excess of 800 children as 'usually one baby a week pops out'.
The use of unlicensed sperm donors has been rising in recent years. This rise is believed to be related to costs involved in using private clinics, and the 2005 change in law that means that people can no longer donate sperm anonymously.
Guidelines set out by the HFEA advise that sperm from one donor should be used to create no more than ten families. This limit is set to reduce the chance of two half-siblings unwittingly starting a relationship together. In addition, research suggests families would be comfortable with this number of half-siblings.
Laura Witjens, chief executive of the National Gamete Donation Trust, is critical of Mr Watson's operations. She told the Victoria Derbyshire programme: 'If you strip it down to bare facts, you have a man who for whatever reason feels they need to impregnate over 500 women; you have women who are comfortable knowing their children have 500 half siblings. In another setting people would be appalled. They would ask questions, find it very disturbing.'
Despite these concerns, Mr Watson does not intend to quit anytime soon. 'Within four years I would like to crack a thousand, if I can. I would like to get the world record ever, make sure no one else is going to break it, get as many as possible.'
Mr Watson is not the only unlicensed 'super donor' who has made a career out of donating. Dutchman Ed Houben has fathered around 100 children using natural insemination. He organises bi-annual events where his children can meet him and holds records of all of his children to reduce the risk of half-siblings starting a relationship.