U.S. Congresswoman Gabrielle Giffords of Arizona was shot at a public event in Tucson, Arizona on Saturday while meeting her constituents in the 8th Congressional District.

After undergoing a surgery for her gunshot wounds in the head, the congresswoman was said to be in critical condition and still " battling for her life," though doctors at the hospital said they are "very optimistic" about her recovery.

This is the first attempt on the life of a U.S. congresswoman, yet only the latest in a long series of murders or assassinations on U.S. presidents, politicians and other famous individuals that have shaken the country over the years.

On Nov. 22, 1963, President John F. Kennedy was shot to death while traveling in a motorcade through the streets of Dallas, Texas. Lee Harvey Oswald was accused of the crime and all evidence pointed to his guilt. He was killed by Jack Ruby, a Texas nightclub owner before he could be adjudicated. Conspiracy theories concerning the murder have not been substantiated.

On March 30, 1981, President Ronald Reagan was seriously injured by a .22-caliber bullet fired by 25-year-old John W. Hinckley Jr., while he was leaving the Washington Hilton in Washington, D.C.. Reagan survived a major surgery to repair a collapsed lung. Hinckley was sentenced to a psychiatric facility.

President Gerald Ford survived two attempts on his life on two occasions in September 1975 in Sacramento and San Francisco, California. Both assassins, Lynette "Squeaky" Fromme and Sara Jane Moore, were subdued by agents before they could open fire.

John Lennon, one of the most politically active rock stars of his generation, was shot to death by Mark David Chapman in New York City on Dec. 8, 1980.

Martin Luther King Jr., one of the most popular advocates of black power, was killed on April 4, 1968, in Memphis, Tennessee by James Earl Ray. Malcolm X, another black nationalist, was murdered on Feb. 21, 1965.

On June 5, 1968, Robert F. Kennedy, then representing New York State in the U.S. Senate, was shot by a killer in Los Angeles shortly after winning the California presidential primary.

In September 1901, President William McKinley died from gangrene that developed from two gunshot wounds eight days after he was shot by an assassin when he was greeting a crowd at the Pan- American Exposition in Buffalo, New York.

Abraham Lincoln was assassinated on April 14, 1865, becoming the first president to be murdered in the U.S. history.