The Superman Curse refers to a theory that is based on a series of misfortunes that have plagued creative people involved in adaptations of superman in various media, particularly actors who have played the role of Superman on film and television.
It's told the co-producer of superman made this curse inside it said:
If you play the strongest man on Earth, you will either die an untimely death or end up in the weakest position possible.
Another factor that attempts to better explain the curse is the "no cape or on-screen time" rule, meaning that actors of the Smallville TV series have not been cursed due to the Superman outfit not being worn, or that voice actors who have played Superman in radio or animated adaptations, namely Bud Collyer and Tim Daly, have escaped the curse.
George Reeves
George Reeves played Superman in the 1951 film Superman and the Mole Men and the ensuing television series Adventures of Superman. Like Alyn, he was recognized only for that role. On June 16, 1959, days before he was to be married, Reeves was found dead of a gunshot wound at his home with his Luger near him. The death was ruled a suicide but other theories persist.
Christopher Reeve
Christopher Reeve played Superman/Clark Kent in the Superman film series, Superman: The Movie (1978), Superman II (1980), Superman III (1983), and Superman IV: The Quest for Peace (1987). The actor was paralyzed from the neck down after being thrown from his horse in a cross-country equestrian riding event on May 27, 1995. Reeve died on October 10, 2004 due to heart failure stemming from his medical condition.
Now all we can be sure, is that this curse is a fake, or that maybe when it finally comes to Tom Welling wearing that suit, he gets adapted to the curse.