I at one point had to say to Rian, 'I pretty much fundamentally disagree with every choice you’ve made for this character. (Mark Hamill)
Chosen One turned into a grumpy and unlikable old man.
Media of Origin:
Star Wars: The Last Jedi
Luke Skywalker is the staple character of the nine Star Wars films. He is portrayed by Mark Hamill. Ranging from being a newborn at the end of the Prequel Trilogy, to the icon everyone knew in the Original Trilogy, to what is effectively a grumpy old man in the Sequel Trilogy. He was flanderized to death in the Sequel Trilogy.
As mentioned above, he is extremely out of character in this film.
This is one of the reasons why Mark Hamill hated The Last JediAMW.
Rather than helping Rey with her training, he nearly refused.
Usually, you saw Luke Skywalker be optimistic, which is what a Jedi represents; regardless of what age they are (i.e. Yoda was older, and he was still optimistic).
In fact, Luke Skywalker can be compared to Superman (DCEU) very easily! Both were iconic heroes who were flanderized from being optimistic, yet still heroic to being grumpy and showing negativity all the time. The only difference is that the former aged, and the latter was always a young man in their respective cases.
When he was handed his lightsaber by Rey, he foolishly threw it right off the cliff.
He didn't bother remembering his twin sister Leia Organa, his best friends Han Solo, Chewbacca, C-3PO, and R2-D2.
There was a disturbing moment where he was milking an alien just for something to drink.
Luke Skywalker was supposed to represent hope, and in fact, A New HopeGMW was referring to Luke Skywalker himself, which is an emotion about showing optimism, positivity, and not giving up even when it seems like it's always lost.
When he faced his nephewKylo Ren, he told him to die, taunted him, and humiliated him as opposed to what he did in Return of the JediGMW where he told Darth Vader (who was one of the most evil guys) that there was still good in him! He even went as far as to try to kill his own nephew!
He died at the end with no proper explanation.
Luke Skywalker was flanderized to the point that even Mark Hamill himself said that the character WASN'T Luke Skywalker at all! This spawned the famous "Jake Skywalker" meme mentioned below.
His actions of sending a image of himself only to die anyway made no sense.
All of the above was done to prop up Rey.
He does not get a lot of screentime in The Rise of Skywalker.
Mark Hamill put in an outstanding performance.
In The Rise of SkywalkerAMW, he told Rey about the error his ways and taught her not to do the same thing.
Although many complain how Luke became so cynical by the time of sequel trilogy, we should note that thirty years passed between Return of the Jedi and The Last Jedi. During this timespan, many things could have happened to Luke and possibly made him lose some of the beliefs he had during the original trilogy. That said, it this is what happened, it should have been depicted onscreen rather than exploring it in spin-off material.
He used to represent hope in the original trilogy along with the tv show, The Mandalorian.
The expanded universe now called Legends did a far better job with the character.
Disappointed long-time fans of the franchise as well as detractors of The Last Jedi have mockingly referred to this particular portrayal of Luke as "Jake Skywalker" after a statement made by Mark Hamill in which he feels this version of Luke is way too different for his liking and says "Maybe he's Jake Skywalker". Since then, the name has been widely used by the Star Wars fandom as a way to express their dislike toward this take on Luke.