William Howard Taft (September 15, 1857 -- March 8, 1930) was the 27th President of the United States (1909--1913) and the tenth Chief Justice of the United States (1921--1930), the only person to have held both offices. Taft was elected president in 1908, the chosen successor of Theodore Roosevelt, but was defeated for re-election by Woodrow Wilson in 1912 after Roosevelt split the Republican vote by running as a third-party candidate. In 1921, President Warren G. Harding appointed Taft to be chief justice, a position in which he served until a month before his death.

Is it true that has a president ever become a supreme court justice?
yes