Ulysses S. Grant was the president of the United States of America from 1869 to 1877. As the head of state, President Grant oversaw all branches of the US government, and most importantly the US Secret Service, with his two top agents being James West and Artemus Gordon, both of whom were one of the few to answer directly to the president and take their orders directly from him. Whenever he appeared before West and Gordon, his life was usually at risk and it was up to his two top agents to save his life and maintain the security and stability of the US.
Grant, West and Gordon have been working together since the Civil War, where West in particular served as one of Grant's top captains in the Union Army. Although Grant probably never knew it, West and Gordon had also saved his life in the past and secured the victory for the Union Army after they were sent back in time by former confederate colonel, Noel Bartley Vautrain, whose nature as an esper allowed him to access the 4th dimension and alter the past, where they stopped Vautrain from killing Grant in an ambush.