Arthur's Legacy

In Stephen King's the Dark Tower, knights have been replaced with the Gunslingers. They are a combination of knight and samurai, but with a western bend in dress, speech, and manners. They are cowboys, essentially. What makes Roland different is that he is a descendant, the last descendent of Arthur Eld, Midworld's version of King Arthur. One concept to remember about the Dark Tower series is that there are people, places and things that resemble our world, but are slighlyt different. The City of Lud, in the Wastelands, looks like New York.
Roland's quest, or grail, is the Dark Tower, the nexus of all space, time and worlds. He must protect it from falling at all costs. What is not his quest, but his obsession is to enter the Tower and see what resides at the top. No one knows what or who lives there, only that the Tower is being guarded by the being known as the Crimson King.
Roland is essentially the final king of all of Midworld. He is also the last Gunslinger. Which is why he trains the three other characters in the novels. He needs backup since his friends have all died. King Never says outright who all of Roland's friends were and how they died, but he does repeatedly mention three. Alan, Cuthbert, and Jamie DeCurrie
That's where the Arthur legend fits in.
Next: The Films of Sergio Leone, specifically the Man with No Name Trilogy...