There are few heroes in the Marvel or the DC Universe that have actually stayed dead, and legendary X-Men writer Chris Claremont wishes that Jean Grey was one of them. Claremont killed off the iconic X-Men member in the celebrated storyline, "The Dark Phoenix Saga", but this death was later retconned so that the character could return to comics in the pages of X-Factor. She was killed again over a decade later.
Fans who follow the X-Men may know that Jean Grey was recently brought back to life. However, Claremont is referring to an event that occurred back in the 1980s. After being consumed by the power of the world-devouring cosmic entity known as the Phoenix Force, Jean Grey lost her self-control and became a threat to the entire universe. She sacrificed herself to save her teammates. Marvel later her brought back by revealing that it wasn't she who went crazy, it was the Phoenix Force. The Phoenix Force had simply inhabited a clone of her body that it had created. Jean's real body was found in a cocoon by the Avengers who reunited her with the X-Men.
In an interview with Syfy Wire, Claremont talks about Marvel's decision to resurrect Jean and why he would have been "much happier" if Jean had stayed dead. Claremont felt that Jean's death had such a huge impact on the X-Men that it should never have been undone when Fantastic Four writer John Byrne decided to retcon it. Claremont was "pissed off" when he found out about it:
That would have been one of those benchmark moments where - because I had played it for the next few years as long as I could get away with it - the other X-Men suddenly realize "We are mortal. We are not protected by the fact that we're all copywritten and trademarked."
Though Claremont saw resurrecting Jean as an "economically justifiable" decision, the writer had other issues with the storyline, particularly concerning her longtime love interest, Cyclops. After Jean's death, Cyclops married Jean's clone, Madelyne Pryor, and had a child named Nathan (who becomes Cable in the future). Claremont pointed out to Marvel that bringing Jean back to life would also resurrect her relationship with Cyclops, which was a "fundamental" problem.
Claremont explained to Marvel that this would lead to Cyclops walking out on his wife and newborn child. Claremont asked Marvel, "What kind of hero would do that?" Unfortunately, the scenario described by Claremont is exactly what happened. Fans have complained for years about the direction Marvel has taken with Cyclops' character development. The hero spiraled downward until his death, and to many fans, the starting point was Jean's resurrection.
Source: Syfy Wire