- Nobody seems to know whether "Xenu" or "Xemu" is the correct spelling. At least, nobody who's willing to talk about it.
- The name of Óðinn/Odin/Oden/Woden/Wotan is spelled differently in basically every Germanic language. This is in part due to Norse having a distinct letter ð for the voiced "th" sound, transliterated in modern English sometimes as th and sometimes as d, and in most Scandinavian languages as dh or d. And the Romans called him Mercury.
- There's also Freyja/Freya/Freia/Freja/Frøya/Freyia. Who is not, however, Frija/Frea/Frigg/Frige/Frigga. (Usually. They are conflated in some versions.)
- God. He's OK with being called God, since it's clear that He's the only one to which a Christian or Jew would refer, but... YHVH or YHWH? Is the name more closely Anglicized as Yahweh, Jehovah, or something in between? It's not supposed to be pronounced. Nobody but the high priest knew how the word is pronounced, and even modern religious Jews misspell it on purpose because they're not allowed to write it. There is some debate about what exactly the word means, but it's likely related to the root 'to exist'.
- Arthurian Legend: Guinevere can be Guenever, Gwenwhyfar, Guenièvre, Guanhumara (!), or Wenneuereia (Flat "What"). Similarly for Isolde / Iseult / Isolt / whatever. It can also be Jennifer or Ginevra.
- Similarly, retellings of the Robin Hood stories often disagree on the spelling of the surname of Robin's Evil Counterpart Guy of Gisbourne/Gisborne/Gisburn etc. Will Scarlet's real family name usually begins with S, but can be Scarlock/Scathelock/Stukely/Stukeley/you-name-it. There's also the Marian/Marion issue. Of course, even among literate people, spelling of names was fairly inconsistent in the middle ages.
- The obscure Catholic Saint Winwaloe. Or possibly Guénolé, Winwallus, Guingalois, or Vinguavally. Or maybe Ouignoualey, or Bennoc, or dozens more.
- The Greek names of figures of Classical Mythology may be subject to this, as Greek has a different alphabet from most other European languages such as English.
- The name of the legendary hero of Greek mythology can be spelled either as Herakles or Heracles. That Other Wiki seems to prefer the latter, as does the Glory of Heracles series. And of course, there's the Roman spelling Hercules, which plenty of other adaptations prefer.
- The three-headed guard dog of the underworld the above had to slay as part of his labors can be romanized as either Cerberus or Kerberos, with the latter being used for a computer network authentication protocol.
- There are multiple accepted ways to write "Hanukkah" in Roman letters. One of the more common variants is "Chanukah".
- There are dozens of different ways to spell "wendigo". About the only consistent traits between the spellings are that most of them start with a W and are three syllables long.
- The Bible, due to the multiple languages in which the original texts were written or translated. It gets worse with some authors, like Yeshua Ben Sira, whose full name is either Joshua Ben Sira, Jesus, the Son of Sirach, Joshua ben Sira, Jesus ben Sira, etc. The Catholic Church decided to avoid this confusion by naming it "Ecclesiasticus", but may have made things worse, since it's often confused with Ecclesiastes.
- The holy book of Islam, given that Arabic script doesn't transliterate very precisely to the Roman alphabet, has been identified as the Quran, Qur'an, Koran, Al-Coran, Coran, Kuran, and Al-Qur'an, among others. Likewise, practitioners of the faith have been referred to both as Moslems (especially in the past) and Muslims, and their prophet goes by a number of transliterations including Muhammad, Mohammad, Muhammed, Mohamed, Mohammed, Mohamad, Muhamed, Muhammet, and Muhamet.
- Lusitanian Mythology: As in many Latinized names, there are several variations to the names; Endovelicus was Aendovelicus and, in Portuguese, Endovélico. There is a possible subversion in Bandua's case as the name Bandus might have referred to the god he/she was consort to.
Spell My Name With An S / Myth and Religion