No such thing as a 6 star General.
Since the British promotion of Montgomery to outrank Eisenhower was the trigger to resurrecting the five star plan, Congress had to expand the five star rank beyond the Chiefs of Staff to include the three major theater commanders, MacArthur, Nimitz, and Eisenhower. The promotion list and dates of elevation, as passed by congress, read as follows:
Fleet Admiral William D. Leahy: December 15, 1944
General of the Army George C. Marshall: December 16, 1944
Fleet Admiral Earnest J. King: December 17, 1944
General of the Army Douglas MacArthur: December 18, 1944
Fleet Admiral Chester W. Nimitz: December 19, 1944
General of the Army: Dwight D. Eisenhower: December 20, 1944
General of the Army Henry H. Arnold: December 21, 1944
So it was that Ike received the fifth star. It placed him among the nation’s most distinguished military officers, along with George Washington, the highest ranking officer in American history, whose title is forever General of the Armies.
The temporary grade of "General of the Army" (five-star) was provided for by Public Law 482, 78th Congress, approved December 14, 1944, and became permanent on March 23, 1946, under provisions of Public Law 333, 79th Congress.