Robert F. Kennedy was a complex figure. Beloved by many, but in many respects he was beloved more after his death than he was when he was alive.
Early in his political career he was known as an avid cold-warrior... secretive, manipulating, and ruthless. A tough little S.O.B. He also authorized wiretaps on Martin Luther King Jr., and reportedly said of King during his brother's time in the White House, "Martin Luther King... Oh, he's not a serious person".
JFK's assasination changed him profoundly (perhaps it was in wondering if his own actions had led to it in a sort of "blowback" operation). What changed him even further were his visits to the poor in Appalachia, Missisippi, and the migrant farm workers he met through Cesar Chavez.
In 1968, he announced his candidacy for the presidency. On April 4, on a campaign stop in Indianapolis, he learned that Martin Luther King had been assassinated earlier that day. He was warned by the police that he may not want to address the crowd, made up largely of African-Americans, who were as yet unaware of the news.
Kennedy decided to go ahead and address them anyway, and to break the news to them himself.
This audio clip is of his impromptu, off-the-cuff speech, which defined his greatest moment.
Quoting the poet Aeschylus:
Even in our sleep, pain which cannot forget
falls drop by drop upon the heart,
until, in our own despair,
against our will,
through the awful grace of God.
Two months later, he himself was assassinated.