Warning! Spoilers for X-Men #1 ahead!
It's been more than 40 years since John Proudstar aka Thunderbird became the very first member of the X-Men to die on a mission, but his sacrifice has not been forgotten. Even though many mutants have been resurrected since the founding of Krakoa, there are still some like Thunderbird who remain dead. The newly launched X-Men series by Marvel Comics specifically references him and indicates that the newest iteration of the team remembers their fallen comrade and wants to honor him.
Thunderbird was first introduced in 1975's Giant-Size X-Men #1 by Len Wein and Dave Cockrum. That issue not only added the most famous X-Man, Wolverine, to the team, but also marks the first appearances of stalwart members Storm, Colossus and Nightcrawler. These "All-New, All-Different" X-Men next appeared in Uncanny X-Men #94, which began Chris Claremont's historic 16-year run on the title and set the stage for the X-Men's dominance in comics for the next 25 years. Thunderbird was a key member of the group, an Apache warrior with enhanced speed, strength and senses known for his combative personality and butting heads with team leader Cyclops. Due to his similarities to Wolverine, and because Marvel wanted to add an element of surprise to this new era of the X-Men, Thunderbird was quickly killed off in Uncanny X-Men #95, dying in a plane crash while trying to stop the evil Count Nefaria.
In X-Men #1 by Gerry Duggan, Pepe Larraz, Marte Gracia, Clayton Cowles and Tom Muller, the team sets up a new treehouse headquarters in New York, which is also said to be a memorial to mutants who did not live to see the founding of Krakoa. Thunderbird is confirmed to be among those mutants as Cyclops gives Polaris a tour of the new HQ. While they are passing the treehouse's hangar deck, Polaris guesses that the team's plane will be called the Blackbird, as X-Men planes have traditionally been known. Cyclops responds, "We're trying to decide between the Thunderbird and the Proudstar. We'd like to honor John's sacrifice."
Thunderbird is unique among X-Men characters (and comic book characters in general) in that he died but has not really been resurrected. He was briefly brought back during the Necrosha event in 2009, and in the Chaos War event in 2010, but both times he returned to the afterlife at the conclusion of the story. And even though the resurrection protocols on Krakoa have made death a minor inconvenience rather than a permanent condition, he has still not returned to the land of the living. The reason for this has not been revealed. It could be that his mind was not backed up by Cerebro, or that there is no sample of his DNA on file — both requirements for bringing a dead mutant back to life.
John Proudstar's death was an important moment in the history of the X-Men. It established that characters could die and that their mission had stakes. Mister Sinister has said that he used Thunderbird's DNA to turn himself into a mutant. And John's brother, James, has been an important character. He first appeared as a member of the Hellions, taking on the Thunderbird name and looking to get revenge for his brother's death. James later took up the name Warpath and joined X-Force. Because death is a revolving door in comics, it's possible John Proudstar could return to life. After all, Count Nefaria was shown to have survived the plane crash. For the moment, however, Thunderbird remains dead, but the latest issue of X-Men shows that his legacy endures.