The Wiki says:
”Aku was the main antagonist of the series Samurai Jack. Born from a cosmic of black mass darkness…” Samurai Jack, Wiki.
Did Aku always exist? Or was he created? Who gave him powers?
I can’t find the answers for these 3 questions.
as per the wiki you linked to Aku came from the Black Mass
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.
the page also indicates it's species as
Primordial cosmic entity
and in the Biography it says
the Black Mass was formed from some sort of explosion that occurred somewhere in the outer space
given that Primordial means "existing at or from the beginning of time; primeval." we can probably assume the Black Mass came from the origin of the universe and the explosion was The Big Bang.
Aku however only appeared after Jack's father tried to destroy the Black Mass with an arrow coated in a magic elixir
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.
so the arrows magic gave the Black Mass the form we see as Aku and it's power to shape shift.
so to answer your questions:
It was explained in Episode XXXVII: The Birth of Evil, Part 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.
So nobody created him on purpose but it just happen from the remaining of space entity black mass.