Big Fish Boss

"Ah, my Fish Legions! Show no mercy! Kill the planet! Kill the planet! KILL THE PLANET! The Galaxy is for Fish!"

- Big Fish Boss ordering the destruction of a planet.

Big Fish Boss is the main antagonist of the entire Ratboy Genius YouTube cartoon show. He is an unrelenting dictator who wishes to become powerful enough to become the leader of the Galaxy - using the threat of absolute destruction.

Personality
While all other Ratboy Genius characters have proven to be sympathetic -- even the villains, with misguided motives and a way of redemption -- the Big Fish Boss is a merciless and terrible warlord who only has one goal in mind: Complete control of the galaxy.

He has absolutely no remorse for anyone else, and is perfectly willing to suck the energy out of stars (hereby killing entire solar systems) to further his own needs. To top that off, he also destroys random planets as a display of power.

He is a great speaker, as shown when he successfully manipulated the entire species of the noble Fish into becoming his mindless soldiers.

He is referred to a being that only wishes to spread mayhem and destruction, and it is established that he is willing to sacrifice any and all of his soldiers, showing that he doesn't even have compassion for his own kind.

Origins
While Big Fish Boss initially seemed to be a demonic, power-hungry creature appearing out of nowhere, it is in a later episode revealed by Ratboy Genius that a previous Fish Boss had attacked Mars, killing all life on the planet and creating what is now known as Valles Marineris. This implies that Big Fish Boss might come from an extremist family of the vague "Fish Boss" line, offering some explanation as to why he is so hellbent on accomplishing his goal.

In Ratboy Genius Dreams Minecraft
While Big Fish Boss does not at all appear in the series, he is implicitly the unseen Bigger Bad; his Cosmic Thunderbolt attack, which would've destroyed Ratboy Genius and co., could only be averted in such a way that the creation of Little King John's world was a consequence of. Therefore, the world that Ratboy Genius explores only really exists because of the Big Fish Boss -- something Ratboy Genius is not yet aware of.

In Galactic Superheroes
The third episode of the series seems to focus on the notorious Fish Eater, who sings about his casual fish eating. The Fish panick and apprise Big Fish Boss about the Fish Eater, and Big Fish Boss becomes the real threat, as he reveals they have a plan to take over the Galaxy.

The furious leader orders his soldiers to tear Fish Eater apart. After this, the Big Fish Boss exclaims the Galaxy is for fish and leaves, not to be seen again for years.

In Starship Genius
In the second episode of the series, Big Fish Boss makes a surprise return, now presented as the main antagonist of the Ratboy Genius universe. Without hesitation, he orders his Legions to destroy an entire planet by repeatedly crying "KILL THE PLANET!" The planet is reduced to dust, and Big Fish Boss, satisfied, stresses that the Galaxy is for Fish. More of Big Fish Boss' cunning plan is revealed in the third episode. The Professor explains that Big Fish Boss, using his Legions, weaves cosmic webs between stars, sucking out their energy to charge up fatal electric bolts which he uses to destroy planets with ease. Eventually, he will have enough power to anihilate the whole of the Galaxy. Armed with this, he plans to become the Leader of everything.

Throughout the episodes, while the Big Fish Boss continues to be a distant force, more is revealed about him, such as his main form of attack, the Cosmic Thunderbolt, and that he manipulates the peaceful Fish into blindly following his orders, causing them to forget they are "noble and free".

He appears in the seventh episode, sporting a new 3D appearance, roaring triumphantly into the sky.

In the tenth episode, while Ratboy Genius is undercover in the Fish quarters, Big Fish Boss appears and holds a mad speech where he promises they will soon take over the Galaxy as his elusive master plan is brought into action. Disgusted, Ratboy Genius leaves along with Summer Solstice Baby.

Quotes
"No! This must not happen! We cannot lose Fish! We need every Fish to complete my master plan!"

- Big Fish Boss' first appearance and line, revealing him as a much bigger threat than the Fish Eater.

"Let's go! Get the Fish Eater! Tear him to pieces!"

- Big Fish Boss chanting as he has his Legions violently mutilate Fish Eater alive.

"Ahh! My Fish Legions! Our time is nigh! Our power is high! The galaxy can hear our cry! We are now ready to complete my master plan! THE GALAXY IS FOR FISH!"

- Big Fish Boss' ominous speech.

"Big Fish Boss in on the move! Nobody's safe! Peril in the Galaxy! Big Fish Boss is a threat to us all!"

- The Galactic Superheroes upon realizing Big Fish Boss has risen.

Trivia

 * While all other Ratboy Genius villains are sympathetic, arguably tragic figures that at some points agree to help the protagonists, Big Fish Boss is absolutely despicable, as he manipulates an entire species, causing them to forget they are free creatures and driving them to suicide in warfare, has his henchmen tear whoever he dislikes to pieces as he eggs them on and orders the destruction of countless innocent planets just to further his own goals.
 * Furthermore, the Big Fish Boss is not even aware of the heroes' existence, cementing him as an unstoppable force of horror.
 * According to Ryan Dorin's Twitter, Big Fish Boss may be a hyper-mutated breed of flounder with a skin disease (a humorous response to an inquiry about his mysteriously flashing body parts).