U.S. Steel
The tower's original name when completed was the U.S. Steel Tower and was changed to USX Tower in 1988. The name was changed back to the U.S. Steel Tower in January 2002 to reflect U.S. Steel's new corporate identity (USX was the 1990s combined oil/energy/steel conglomerate). Although no longer the owner of the building, U.S. Steel remains one of the largest tenants.