Professor Charles Xavier has a lot of defining features: his telepathy, being in a wheelchair, mentoring many incarnations of the X-Men, etc. However, physically he's almost always bald. The reasons for him rocking the chrome dome vary, but with some exceptions, you can usually count on seeing him without hair. However, for the upcoming Logan, Patrick Stewart's Professor X has actually grown back a little hair in his elderly years, and according to director James Mangold, the reason for the growth is due to the mutant's deteriorating mental condition.
While admitting that giving Professor X hair "could be kind of sacrilege," James Mangold told Empire Online that the reason for the character's altered look in Logan was to reflect his poor health. Mangold said:
The theory was that he originally lost all his hair because it's just too damn busy [in his head] to grow hair -- the idea for me was, well, maybe there's a little fringe on there, because things are slowing down mentally.
The sight of a Charles Xavier with hair actually hasn't been that odd in the movies in recent years, as James McAvoy's iteration of the character had hair during X-Men: First Class, X-Men: Days of Future Past and most of X-Men: Apocalypse. However, during that last movie, it was revealed that he went bald when he was forced into Apocalypse's body transfer ritual. He was saved before the process was complete, but he's lacked that glorious mane ever since. So James Mangold's theory isn't on the mark, but given that Professor X is also the world's most powerful telepath (well, when Phoenix isn't around, anyway), it's plausible that because he frequently used his telepathy, that prevented the hair from ever going back. It's doubtful this will be directly addressed during Logan, but it's interesting to think about.
It's been confirmed that Logan takes place in the year 2029, meaning that Professor X will be nearly 100 years old. Although he appears to still have some of his mental abilities, he's sadly become unstable in his old age, and Wolverine and Caliban are looking after him. While Logan marks Hugh Jackman's final performance as Wolverine, this might also conclude Patrick Stewart's time with the franchise, leading some fans to wonder if Professor X might die during the movie. That remains to be seen, but from what we've seen in the trailers so far, even with his mental issues, Charles Xavier will be an important person in Wolverine's life. It also looks like he'll be the one who pushes Logan to take Laura, the young girl very much like him, under his wing. He may not be leading the X-Men anymore, but he's still proving to be a welcome ally.
Logan claws its way into theaters on March 3.