|“||Power only has meaning if it's put into action... it defines you. Power like that is what rules the world.||„|
|~ Seth to Ryu.|
|“||Etch my name upon your soul, and know that the one who killed you is called Seth.||„|
They appear as NPC and the final boss of the arcade version of the game, an unlockable playable character in the console versions of Street Fighter IV, and a playable character in Super Street Fighter IV.
They are voiced by Akio Otsuka in the Japanese version, and by Michael McConnohie in the English version.
Bearing silver skin and an extremely muscular physique, Seth is a synthetic human that lacks clothing or hair; whether they is an android or cyborg is unclear. In their abdomen, enclosed inside a pattern consisting of the Eight Trigrams of Taoist cosmology, is an exposed area, which contains a rotating sphere known as the Tanden Engine, which appears to be the source of his power.
Seth is just as intelligent as M. Bison himself, with ruthlessness and evil to match despite not playing as big of a role. Unlike M. Bison, Seth is generally very calm and concise, though their displays a fair bit of arrogance, often through their annoying-by-design tendency to laugh and gloat when using their more powerful moves. Seth also demonstrates a deep knowledge of the philosophy of human nature and the pursuits of purpose and self-awareness. This unusual trait, coupled with their endless thirst for power, implies that Seth intends to become their own entity entirely and not be bound to M. Bison as his replacement shell. Notably, while Seth appears to be the only "sentient" enhanced being, their Arcade Mode win quote against another Seth implies that at least one other clone may have developed self-awareness.
However, their desire for power and his philosophical pursuits are a one-sided and neutral affair; their displays very little (if any) morality or respect for life, and values people only for their usefulness to them. Due in part to their ego, Seth will keep their S.I.N. subordinates in the dark in case they plan to betray them, as insubordination is something they refuse to tolerate. Seth is of the belief that any power is good power, as indicated during his fight with Ryu in the animated film. In addition, despite their philosophical leanings, Seth displays some form of disbelief in the mystic arts; their Arcade Mode win quote against Dhalsim states that if the latter's techniques were truly mystic, they could not possibly imitate them.
Ironically having a martial arts symbol to represent themselves, Seth is one of the least honorable characters in Street Fighter, with their ability to absorb other fighters, they copies their abilities, skills, and even iconic attacks such as the Shoryuken and without even training for them at all. This makes them among the dirtiest fighters in the series.
Seth has a mad lust for power, doing anything what so ever in order to gain it, even so much as to torture, such as when they tortured Dan Hibiki for the Satsui no Hado. They don't even care what people think of their methods, because Seth believes that it does not matter what humans think is evil. Power is all that is truly important to him.
Street Fighter IV
Seth is the 15th of 26 enhanced beings that use data collected from the world warriors to create a deadly style of mixed martial arts. Seth claims to be superior as a result of their humanity while the others are merely puppets. Their storyline indicates that their plans to control the remnants of Shadaloo through S.I.N after M. Bison's apparent death at the hands of Akuma in Street Fighter II. They also attempts to manipulate Juri Han, a woman who possesses a bionic eye they created. She confronts them and unexpectedly offers to work for them, to which they agrees. They host a World Warrior tournament in hopes of luring Ryu to complete their BLECE project, but is dismayed at reports that Bison has once again returned from death. Bison finally encounters Seth and defeats them in combat, and afterwards tells them that in fact everything that has happened has gone according to Bison's plan. After Bison leaves, Juri tells Seth that she intentionally pitted the two against each other, but is disappointed that Seth was not more of a challenge for Bison. Afterwards, Ryu would encounter another Seth and defeat them and destroy the BLECE machine. Bison commands the remaining copies of Seth and they wreak havoc on the fighters in and around the S.I.N. compound, as many of the characters' endings depict them defeating a version of Seth.
Street Fighter V
Seth returns in Street Fighter V, this time possessing one of the Dolls for their body.
Project X Zone
Seth makes an appearance in Project X Zone as a unplayable boss.