Muhammad Ali, the reigning world heavyweight boxing champion, entered the combative ring of politics and culture by refusing to
serve in the United States military at the height of the Vietnam
War on this day in history, April 28, 1967.

"I ain’t got no quarrel with those Vietcong," Ali famously said the
year before, the exact quote the source of some dispute, in a
battle that made it all the way to the United States Supreme
Court. The Vietnam War was at its heights at the time.
Fox News

Ali was convicted and given five years in prison for refusing induction in to the United States draft as mandated by the Selective Service Act.