[6][7][8] With his expertise in Science, Mathematics and Economics, Castle co-founded the institutional private equity market in the late 1960s.

[9] Throughout his career, he has been the owner and controller of the following corporations: Delaware Management, Ethan Allen, Ames True Temper and several restaurant chains (including Perkins, Marie Callender's and Morton's Steakhouses.

[12] In 1969 – as chairman of DLJ's Merchant Banking and Sprout Group – Castle was a pioneer in the promotion of the use of limited partnerships as a means for pension funds and other large institutions to invest private capital into companies.

[16] Castle has a Bachelor’s Degree from the Massachusetts Institute of Technology, and an MBA from Harvard Business School where he was a Baker Scholar with High Distinction.

In May 2015, Castle and his wife, Marianne, sold the estate for $31 million to TGS Florida LLC, managed by Jane H. Goldman of New York.