Kingdom Hearts Riddles IV

[TwilightLord]

Why do you think it's Xehanort?

EDIT: Okay, this thread has gone forever with no one guessing, so I'm just gonna reveal the answer.

The answer I was looking for was Ansem, Seeker of Darkness. Here's the reasoning.

I might be a song,
But something feels off about it.

This is actually a bilingual pun. "Ansem" is written "Ansemu" in Japanese phonetics, which is the same way the English word "anthem" would be written.

I might be a human,
But I lack something important.

He's a Heartless, so though he has a human form, he lacks something (i.e. a heart).

I might be the end,
But I am also the beginning.

He is the final boss of the first game, but the first game is the start of the "Xehanort Saga" according to Nomura, so Ansem/Xehanort's Heartless could be said to be starting off the series.

I might be powerful,
But I am not invincible.

Speaks for itself. He's powerful, but Sora is still able to defeat him.

I might be defeated,
But I am not gone.

After his defeat at the end of Kingdom Hearts, he still lurks inside Riku's heart and shows up as the main villain of Reverse/Rebirth mode in Kingdom Hearts Chain of Memories. After that, Riku is able to use his power and change his appearance to that of Xehanort's Heartless in Kingdom Hearts II and Kingdom Hearts 358/2 Days. Xehanort's Heartless also appears as a villain in Kingdom Hearts 3D: Dream Drop Distance.

I might be wise,
But I am merely a player.

The real Ansem is known as Ansem the Wise. "Player" here is used as a synonym for "actor", referring to how Xehanort's Heartless is "acting" as Ansem, stealing his name and identity.

I might be known to you,
But can you tell me my name?

The name is Ansem, a.k.a. Xehanort's Heartless.

If anyone still actually goes here, then you can take the next riddle.