Henry Kissinger once received the Nobel Peace Prize for failing to negotiate a peace treaty. Which tells you close to everything you need to know about the man: he is lauded out of all proportion to his actual achievements. Realistically, his single greatest achievement is avoiding prosecution in the downfall of the Nixon administration.
I’ll back up. Kissinger was Nixon’s Secretary of State and later his National Security Advisor. As such, he was a major architect of America’s involvement in the Vietnam War (and thus, of America’s defeat in the Vietnam War). A proponent of Realpolitik (which is basically the doctrine that morality comes second to winning in politics), Kissinger was not a bloodthirsty man, but a callous and indifferent one. If other people had to die for him to get what he wanted, so be it.
He remained in office throughout the Ford administration, while he largely disappeared during the Carter years, Reagan relied on him for advice, as have almost all his successors in the Oval Office. Kissinger is still seen as an authority on US foreign relations even today – in 2016, Clinton boasted that he was one of her advisors (and Sanders boasted that Kissinger was not, and would never be, one of his advisors).
As mentioned in:
Henry Kissinger — Monty Python