He founded, co-founded, or was a major investor in companies including Ensco plc, an offshore drilling company, in 1986; Columbia Hospital Corporation in 1988; Mid Ocean Limited, a provider of casualty re-insurance, in 1992; Crescent Real Estate Equities, Inc. in 1994; and Pioneer Natural Resources in 1997. In 2010, he was awarded the Arbuckle Award at Stanford, where he received a MBA in 1968. In accepting the award, he credited his mother with giving him people skills that had an enormous effect on his Business and deal making success.
The son of a wholesale grocer, Rainwater grew up in Fort Worth, Texas. He is of Lebanese roots. He graduated from the University of Texas at Austin with a degree in mathematics, where he was a member of the Tau chapter of the Kappa Sigma fraternity. He was recognized by the national organization in 1996 as Kappa Sigma Man of the Year. After graduation, he went on to earn a 1968 MBA from Stanford Business School.
In 2009, he was diagnosed with progressive supranuclear palsy.
In March 2011, a court declared him incapacitated, and his youngest child, Matthew, became his legal guardian.
Rainwater died on September 27, 2015 from progressive supranuclear palsy, aged 71.