JFK beat Nixon in a close race to become our 3rd President to serve during the cold war.
Most of what JFK was notable for dealt with foreign affairs. For example one of the first things that happen was the Bay of Pigs invasion. Where the CIA had trained Cuban rebels to overthrow the Castro-Communist government. Needless to say, that plan flopped pretty hard.
The Cuban Missile Crisis had the world on the edge of it's toes over the thought of nuclear war. Thankfully it ended with both sides making compromising and removing nukes close to their rival's homelands.
JFK also had a lot to do with the prevention of Communist countries such as Laos and Vietnam. At least he didn't mess things up as badly as LBJ did.
I do have to thank him for the creation of the Peace Corps which still operates and helps many today.
He also helped hurl us into the Space Race when we were lagging behind the Soviets. Might seem kinda silly today, but it really helped boost American morale back then.
JFK was a friend to civil rights, and did a lot to help the cause. Granted he did wait cautiously for fear of the racist Southern Democrats (most of whom later switched to the Republican side) trying to block all his civil rights bills.
Of course it all ended short when JFK was assassinated by Lee Harvey Oswald in Texas.
As for Oswald, I believe if he wasn't acting alone then he was working for some criminal mafia-type group. Maybe he worked as one of their thugs and perhaps they didn't want him to link them to the death of a U.S. president. Which pretty much meant that whole police force on all levels would hunt you down.
I think JFK was a good president, however I think his legacy is a bit heightened because his reign was cut short too soon.