Sergei Khrushchev was the son of former Soviet leader Nikita Khrushchev. He eventually turned against communism and settled in the US. His ideological conversion apparently began when he visited the US with his father in 1959.
In the Washington Post and indeed other news reports of his death, Sergei reportedly died of a gunshot wound to the head, but the police do not suspect "foul play." That means he either committed suicide (he was 84 and had health issues), or (less likely) accidentally shot himself.
At this stage, we cannot completely rule out the scenario of an assassination ordered by the Kremlin. Sergei and other members of the Khrushchev family have been publicly critical of the Putin regime, and Putin has previously targeted Russian opponents of the regime living in the West. As always, however, it is best to reserve judgement until we know more.
While I respect Sergei and other members of the family, I do not fully share the favorable views of his father many in the West have. It is indeed true that Nikita Khrushchev liberalized many of Stalin's most repressive policies, and freed many political prisoners. But, under his rule, the USSR remained a brutal totalitarian state, even if less awful than under Stalin.
Moreover, Khrushchev was himself deeply complicit in many of the atrocities of the Stalin era, particularly when he was the communist party boss in Ukraine in the 1940s. It was as if Hitler's regime survived WWII, and Hitler was then succeeded by some other high-ranking Nazi, such as Goering, who then proceeded to liberalize the regime, while keep its essence intact. Khrushchev is also to blame for nearly provoking a nuclear war, and for the construction of the Berlin Wall, among other things. Obviously, none of this reflects on his children and grandchildren, many of whom seem like admirable people.