The Death and Return of Superman story arc, after a deadly battle with Doomsday, Superman died in Superman #75 (Jan. 1993). He was later revived by the Eradicator using Kryptonian technology.
In Superman #52 (May 2016) Superman is killed by kryptonite poisoning, and this time he is not resurrected, but replaced by the Superman of an alternate timeline.
The first story in which Superman dies was published in Superman #149 (1961), in which he is murdered by Lex Luthor by means of kryptonite. This story was “imaginary” and thus was ignored in subsequent books.
In Superman #188 (April 1966), Superman is killed by kryptonite radiation, but is revived in the same issue by one of his android doppelgangers.