Presidents who were members of the KKK:
President Warren G. Harding, President Woodrow Wilson, President McKinley, President Calvin Coolidge, and President Harry S. Truman.
Supreme Court Justice members: Hugo Black.
Other notable and downright important men were: President Warren G. Harding. He was actually sworn into the Ku Klux Klan in a Klan ceremony conducted inside the White House by Imperial Wizard Colonel Simmons.
President Woodrow Wilson and President McKinley were members of the KKK, little is known of their Klan membership however. There is at least one book that documents they were actual members, but it only mentions they were members, that's all. McKinley was a Union officer, but many Union men joined or affiliated with the original First Era Ku Klux Klan during the Radical Republican's anti-white Reconstruction Era. Union General Hardee was another Union man who later joined the Klan. President Wilson would have been a member of the Klan under the Command of Imperial Wizard Colonel Simmons.
President Calvin Coolidge was a noted Klansman and was well known to be an active member of the Ku Klux Klan. He allowed cross lightings on the Capitol steps and reviewed the giant Klan parades of 1925 and 1926 in Washington D.C.
President Harry S. Truman was a minor ordinary Klansman from 1920 - 1922. His two year membership was not notable and somewhat lacking. He eventually had a major falling out with the KKK over his desire to appoint RomanCatholics to key political positions; something which all of the KKK opposed at the time. Some Klans now not only accept Roman Catholics but actively recruit them. The true Ku Klux Klan is however traditionally and rightfully opposed to Roman Catholicism and Papists influence over America. President Harry S. Truman was currying favor with Roman Catholic voters and was more interested in his political career than the Klan or the good of America. He severed all ties with the KKK and openly repudiated them. They didn't call the arrogant upstart "give them Hell Harry", for nothing. His family has tired to deny his KKK membership ever since, but has failed miserably since it is a well established fact of documented history.
Supreme Court Justice Hugo Black was a Klansman, his Klan Robes complete with his name in them were found in an old Klan Klavern Hall in the 1960's. Unfortunately under intense political pressure he superficially repudiated the Klan during its notorious period of scandals.
Gutzon Borglum the artist who carved Mt. Rushmore, Stone Mountain, and also did work on the base of the Statue of Liberty was a prominent Life Member of The Ku Klux Klan. He sat on the Imperial Koncilium in 1923, which transferred leadership of The Ku Klux Klan from Imperial Wizard Colonel Simmons to Imperial Wizard Hiram Evans. Later while under intense pressure and scrutiny, both public and media pressure worked their wicked results and he superficially repudiated The KKK.
The list continues:
http://kelticklankirk.com/KKK_Wizards_and_Prominent_Klansmen.htm