Although the most visible role of the Secret Service is to protect the current and former presidents and first families, as well as other important members of the Executive Branch, its history and mission is much broader. 
At first, White House security was relatively informal, and local police forces often offered protective services. This included local Washington, D.C., officer John Frederick Parker, who was assigned to guard President Abraham Lincoln at Ford’s Theater on April 14, 1865.
President Lincoln’s assassination that night highlighted the need for increased presidential security, but when the Secret Service was established on July 5, 1865, its original mandate was to investigate counterfeit currency and support the U.S. Marshals Service.
Two more presidents would be assassinated—President James A. Garfield in 1881 and President William McKinley in 1901—before Congress requested that the Secret Service provide protection for the president in addition to its other duties.
Although the request originally only included the president, protection was extended to the first family in 1917, to the vice president and the president-elect in 1951, and to presidential candidates following the 1968 assassination of Democratic candidate Robert F. Kennedy.
In 1981, two Secret Service agents prevented the assassination of President Ronald Reagan in Washington, D.C. Upon hearing shots, Agent Jerry Parr shoved the president into the waiting car, while Agent Tim McCarthy threw himself in front of the president, taking a bullet for him.
President Reagan, White House Press Secretary James S. Brady, and local police officer Thomas Delahanty were also wounded, but all four men survived the attack.
“He made himself bigger than life and interposed himself between the assailant and the president,” Parr later said of Agent McCarthy. “He probably saved the president's life or my life.”
