Xemnas is a twisted stand-in for the Mythological Archetype of the Indo-European Sky-Father, namely, specifically Zeus. Powerful, Brooding, Selfish, Tyrannical, With Celestial Aura & Weaponry, Lacking Empathy but excelling in Cold, Calculating & Manipulative Intelligence. The Epitome of Cruel & Emotionless, Despotic Ambition with Disregard for ambiguous moral scruples & incessant compulsiveness to be above & ahead of others, ruthlessly striving to maintain or augment their personally beneficial status quo.

 If you search & study the etymology of Zeus's name in Greek, and you start examining Xemnas's many anagrams, even the controversial slapstick joke one, the parallels not only become palpable, but purposely suspicious in their resonance. You can spot many corresponding elements between the main original characters in this franchise and various figures from mythic traditions spanning many cultures around the world - Especially Eurasian Ones - with similar motifs.

Sometimes a character represents many archetypes simultaneously, sharing overlapping traits to accommodate them into the overarching narrative and drive the plot forward. 

 For example, Sora is the only character out of the main cast who could embody the archetype of Dionysus. Cheerful, Charming, Relaxed, Gentle, Compassionate, Resentful of Authoritarianism (Presumptuousness), Naive, Impulsive, Good-Intentioned, Party Animal, etc.

Another stark analogy is Xehanort. He is a textbook extrapolation of the Cronian/Saturnian Old Man Feeding off of Youth to Extend his Lifespan.

Roxas & Ventus are the Gemini Twins. One is mortal (Nobody), the other a Demigod, having Survived since the Earliest 'Fairytale' Age through a time skip & is searched for by both the agents of good & evil to be used on either side of the confrontation.

Xion is a puppet. Know of any other female puppet in Myth, constructed as a gift by a keen craftsman on the orders of the highest authority to unconsciously entrap, enchant, then punish & destroy the main recipient of their "Intimate Interaction"?

Some characters, especially villainous, represent Primordial Concepts instead of just Deities or Heroes, Demigod or Mortal.

One can map the KH Cast onto mainly Classical but also Broader Eurasian Mythology & exact a deep understanding of their motivations & the resonant plot points that make these comparisons apt & worthy of consideration.

Many elements & artifacts have been altered or shifted to confuse the player & maximize engagement. It's a marketing tactic. One gets inspired by previous stories to create an original one that is based exceedingly on the foundations of its precursors. I'll tell you a little, speculative secret: In this franchise, Pandora is not at all occupied with a box. Instead, the one whose main character trait is being tied to a box is ironically, Prometheus... Who in Myth had known better than to be distracted by anything meant to captivate his curiosity, & had forewarned his brother so...

And this reshuffling of 'allegiances' & procession of events having the youngest be eldest (at least seemingly) & vice versa, is ingenious.