Martin Luther King, Sr. was given the name Michael King at birth. Shortly after touring the Holy Land, he changed his name to Michael Luther King, and then to Martin Luther King. (This source seems to be what other sources I've been able to find are based on.) This changes gave him the initials MLK, which is familiar to students of Semitic languages as something of a pun: the root M-L-K means “king” (מלך, ملک; no, Semitic roots are not that straightforward, I'm simplifying). It's possible of course that this was a coincidence, but given that Martin Luther King, Sr. was a minister, and that he had just been on a trip to the Holy Land (where he might have studied some Hebrew, if it hadn't studied it already), it seems like it might have been intentional.
Are there any documents supporting or refuting this idea?
Edit: Based on some of the comments, I believe it may not be clear that I know that Martin Luther the most famous Protestant theologian in history. Undoubtedly the “Martin Luther” part comes from that; that is not a competing hypothesis. The cleverness of any pun comes from its multiple semantic and phonetic associations. The question is whether there are documentary sources, closer to the event, showing that MLK, Sr. was aware of the potential for this pun. Examples would be letters that he wrote, or contemporary sources commenting on the pun, such as might suggest that the pun was understood and/or intended by MLK, Sr.
Edit 2: This has been a frustrating experience, but I'll just offer one further clarification for anyone who might be interested. This business about Hebrew/Semitic roots having particular meanings does not require the least expertise in the language. It's the kind of general knowledge feature of the language that would be covered in the first couple chapters of a book on Hebrew, or even in a course that touched only tangentially on Hebrew. (I believe my first exposure to the idea was in a course on Middle Eastern humanities, for instance.) So this doesn't require some obscure knowledge of Hebrew; it's a commonly discussed feature of the language.