A typical, mechanized Foot Soldier.
The Foot is an ancient ninjutsu clan, founded in Japan in 1583.
History
The Shredder, followed by the Turtles and Splinter, went back in time to try to kill the creator of the Foot Clan. In 1583, Shredder's ancestor Oroku Sancho led a small group of samurai, and Shredder offered to help him find magical artifacts that would give him power and wealth beyond his wildest dreams. Meanwhile, Splinter's ancestor Hamato Koji had been sent to find the same artifacts, and did find them with the help of his descendant and the Turtles. One of the artifacts released a dragon, which headed for nearby villages; Splinter and Koji went to stop it while the Turtles went to fight Shredder. Sancho's men captured the Turtles, and were about to execute them when Koji arrived, riding the dragon, which he had tamed. Seeing this, Sancho fled in fear, and Koji offered to lead Sancho's men and teach them the ninjutsu art of Shibana-Sama, founding the Foot Clan, so named for the footprint of the dragon in which he stood as he made his speech. (However, according to "Blast from the Past", Shibana-Sama originally founded the Foot Clan.)
In 1960s Japan, both Oroku Saki and Hamato Yoshi were part of the Clan. Saki framed Yoshi for trying to kill a visiting sensei and had him exiled to New York City, thus clearing the way to take over the Foot Clan. He then proceeded to turn the Foot Clan into an army of criminals.
Over the years, Saki, who became known as The Shredder, moved to the USA, allied himself with the alien warlord Krang, and replaced the human Foot Ninja with robotic Foot Soldiers. However, these robots are no match for the Ninja Turtles who destroy them at every encounter.
In the cartoon, The Shredder once considered making more intelligent Foot Soldiers, capable of learning and taking decisions by themselves. However, the idea was quickly abandoned when the first intelligent prototype, named Alpha One, rebelled against The Shredder.
The Foot Clan's logo is a drawing of a right foot, and the Foot Soldiers wear purple and black uniforms featuring the logo on their foreheads. The Foot logo can also be seen on the Technodrome.
The Foot Robot concept allowed the Turtles to destroy the Foot soldiers without any moral thoughts, allowing Leonardo and Raphael to use their weapons more offensively. Meanwhile the series could keep its younger audience and remain a "family show". This principle also benefited the video games.