In the movie Watchmen Nixon is referred to as Tricky Dick. I'd like to know a bit more about the origin of the term and if it can be used in context other than just when talking of Nixon?
Tricky Dick refers specifically to Richard Nixon, and when applied to other people, it is to disparage them by association or comparison with him.
Rep. Helen Douglas, Nixon's opponent in the 1950 campaign for U.S. Senator from California— remembered as one of the bitterest ever— is credited with coining the nickname in a speech, disparaging his ruthlessness and unscrupulousness with political opponents. It was popularized in a subsequent Democratic Party advertising campaign.
Of course, Nixon is not alone with his disparaging moniker; of recent vintage we have Dubya for George W. Bush and Slick Willy or Bubba for Bill Clinton, but wags have been nicknaming the president at least since His Rotundity John Adams.