Number one overall and in politics definitely has to be LBJ. Civil rights and Vietnam, at the same time as relations first warmed and then really cooled with the Soviets.
Obviously MLK is there, but I think less important than LBJ.
Nixon is another huge one, both for ending Vietnam and destroying the power and prestige of the Presidency by abusing it (or, at least, being caught abusing it). Also, he began to normalize relations with China.
Henry Kissinger, who so espoused realpolitik and was able to negotiate a settlement between Israel and its Arab neighbors despite being a Jew.
Zbigniew Brzezinski, who was a hawkish Democrat in the increasingly dovish Carter administration, whose presence weakened the Democratic Party which contributed to its defeat by Reagan's Republicans, who in turn espoused Brezinski's hard-line stance against communism. Brzezinski was the driving force in the Carter administration to establish full diplomatic contact with communist China.
Robert McNamara, defense secretary under LBJ, who mis-handled the Vietnam War and meddled too much on operational and even tactical levels. His failures are what inspired later Chiefs of Staff to clarify the requirements for successful war in a political world full of media perception, which reached its peak as the
Powell doctrine. McNamara was also the first to use, at least formally, the term "mutually assured destruction", referring to the guaranteed counter-strike to destroy the Soviet Union if it attacked, or vice-versa. This was made possible by the emergence of nuclear submarines which could survive a pre-emptive strike.
Pat Robertson/Jerry Falwell for kickstarting the evangelical movement and enmeshing it deeply with politics.
Thomas Watson Jr., the man who took IBM into the computer age.
Creighton Abrams, for starting the Army on the path towards an all-volunteer force.
Bill Gates, for obvious reasons. His charity work, his software empire that united what could have been a very disparate set of computer standards, etc.
William Shockley, John Bardeen and Walter Brattain for the creation of the first practical
transistor.
Andy Grove and Gordon Moore, the two most active Intel co-founders.
Alfred Kinsey, for breaking America out of its puritanical attitudes towards sex and beginning the sexual revolution.