Well, Reagan does get some of the blame. He made changes to tax policy in 1986 which caused companies to replace non-wage compensation (e.g., company cars) with taxable income.

Since taxable income is included in inequality statistics, but company cars are excluded, this caused a big spike in inequality in 1986.

http://www.scottwinship.com/1/post/2011/03/what-would-it-mea...