Final answer:
The creator of the Manberg War Flag, a black flag with a red 'X', is not referenced in historical contexts and does not have a verified creator based on the provided references about flag history and design.
Step-by-step explanation:
The Manberg War Flag, described as a black flag with a red 'X' through the middle, appears to refer to a fictional or non-historically documented flag. This indicates that the flag does not have a verified creator within a historical or vexillology context, unlike flags such as those designed by Gilbert Baker or referenced by historical movements. The mentioned sources discuss various flags representing different historical, social, and political movements from the use of a red flag to symbolize communism during the Paris Commune, to Jasper Johns' artwork on the American flag, and even the new Mississippi state flag designed by a team including Rocky Vaughan.
Confirming the creation of the Manberg War Flag would likely involve a search outside mainstream historical or politic domains, possibly in literary works, video games, or online fictional narratives. Therefore, the answer to who created the Manberg War Flag is not found within the historical context provided in the references given.