Aku foi criado? Se sim, quem o criou e lhe concedeu poderes?

de acordo com o wiki que você vinculou ao Aku, veio da Missa Negra

The Black Mass, also known as The Ultimate Evil, was a non-sapient life form that roamed outer space, and is presumed to have been an organic manifestation of pure evil, perhaps even the source of evil itself. Before it could fulfill its purpose, which was likely to devour all of creation, three deities: Odin, Ra and Rama arrived to exterminate this great evil. The surviving remnant of the Black Mass that escaped the confrontation eventually landed on Earth and would later spawn the demonic sorcerer known as Aku.

a página também indica sua espécie como

Primordial cosmic entity

e na biografia diz

the Black Mass was formed from some sort of explosion that occurred somewhere in the outer space

dado que Primordial significa "existente desde ou no começo do tempo; primitivo." provavelmente podemos supor que a Missa Negra veio da origem do universo e a explosão foi o Big Bang. / p>

Aku no entanto só apareceu depois que o pai de Jack tentou destruir a Missa Negra com uma flecha revestida em um elixir mágico

Unexpectedly, the poison arrow's magic had the unforeseen effect of galvanizing the evil mass into a humanoid form, giving it intelligence, sentience, and shape-shifting abilities.

Então as flechas mágicas deram à Missa Negra a forma que vemos como Aku e é poder mudar de forma.

para responder às suas perguntas:

• Aku foi criado a partir da Missa Negra, mas a Missa Negra existe desde o início
• Aku teria ganho seus poderes da Missa Negra com a exceção da mudança de forma que ele obteve da flecha que tentou destruir a Missa Negra

Foi explicado em Episódio XXXVII: O Nascimento do Mal, Parte 1

In The Birth of Evil Part 1, the Black Mass was formed from some sort of explosion that occurred somewhere in the outer space. When it set off to find its prey, most likely the universe itself, Odin, Ra, and Vishnu arrived to exterminate the mass. After a fierce battle, the three gods finally defeated the Black Mass. Unfortunately, it was not completely destroyed; a fragment of the black mass drifted away from the battle unobserved and crashed into the Earth approximately 65 million years before the rise of Aku. The subsequent impact is believed to have triggered the Cretaceous-Paleogene extinction period, more commonly known as the event which wiped out the dinosaurs.

As life on Earth began to evolve anew, many people were devoured by the mass as it expanded, likely in an attempt to regain its lost power and essence. When the creature approached Feudal Japan, the Emperor (Samurai Jack's father) attempted to destroy the Black Mass with a magical arrow. However, rather than purging the evil from his land, the arrow's poison instead caused the Black Mass to gain intelligence, self-awareness and consciousness, becoming sapient and being set free from the ancient tar pit. Taking the name Aku.

Então, ninguém o criou de propósito, mas acontece apenas com o restante da massa negra da entidade espacial.