I see you've already got an accepted answer, but I don't find it satisfactory, at least for US usage.
It's Always Been Used in America... Sort of
"Czar" as a word being synonymous with authoritarianism or a dictatorial style has been a part of the US as long as there has been a US, with early politicians leveling the term at each other off and on. So it's always been in the US vocabulary.
Enter Judge Landis
After the 1919 Black Sox World Series scandal, the owners of baseball needed to clean up their sport. Ultimately, they decided that Federal Judge Kenesaw Landis was the man to do it. He became the first commissioner of Major League Baseball, with a broad set of powers the leaders of baseball before him didn't have. Ultimately, he was nicknamed the Czar of baseball, both because he wielded his power heavy and often, and because he came into conflict with one of baseball's biggest stars, Babe Ruth, "The Sultan of Swat." Newspapers simply couldn't resist headlines like "The Sultan and the Czar." It was a great title to contrast the popular Ruth with the skepticism people had for the job Landis would do as baseball commissioner.
He did a much better job than people expected, however.
By the time Landis died in 1944, he had done a tremendous job cleaning up baseball, had become immensely popular, and had turned the nickname "Czar" into a much more positive one. Throughout the 30s and 40s, Czar had entered the American political sphere as someone who accomplished difficult tasks and wields power effectively rather than the authoritarian meaning it had before.
Edit: I just realized that I'm on the politics stack and not the history stack. I'm going to leave my answer up, but it's probably better suited for that community.