Which aircraft was originally nicknamed the "sacred cow"?

As the only VC-54C built, the aircraft was heavily modified on the assembly line. A C-54A fuselage was fitted with wings from a C-54B which offered greater fuel capacity. The unpressurized cabin included an executive conference room with a large desk and a rectangular bulletproof window. For additional comfort, a private lavatory was installed next to the president’s seat, and a fold down bed was concealed behind the sofa. An electric refrigerator in the galley added an uncommon luxury for 1945. A battery-powered elevator was installed at the rear of the aircraft which allowed President Roosevelt to board the aircraft easily while in his wheelchair.