In 1953, Ainsworth founded Sydney-based Aristocrat Leisure, a gambling machine manufacturer, which has since grown into the second-largest gaming machine company in the world. Although Ainsworth stepped down as head of the company in 1994, he later founded, at the age of 72, Ainsworth Game Technology, where he remains executive chairman. Now 93, Ainsworth has focused his philanthropy over the last fifty years on the fields of pediatric medicine and medical research, as well as higher education, especially the field of engineering.
According to Forbes, Ainsworth quietly gave a large stake in Aristocrat Leisure to his seven sons and wife twenty years ago and, with recent disclosure of that information, no longer ranks as a billionaire.
"As a private person, I prefer to minimize publicity of my philanthropic activities but at the same time," Ainsworth wrote in his pledge letter, " [I] realize that setting a positive example is the best way to encourage others to give back."