Project Caliban, aslo referred to as the Protomolecule project, was an attempt by Mao-Kwikowski Mercantile to create human super soldiers. The project was ultimately backed by the Martian government as means of asserting their dominance over their stronger rival, the United Nations. The project was, however, uncovered by Chrisjen Avasarala, and the MCR lost their partnership with Jules-Pierre Mao after the death of Defense Minister Pyotr Korshunov. UN Undersecretary Sadavir Errinwright renewed his alliance with Mao for the good of the United Nations, with the former allowing the continuation of the project.
By infecting humans without immune systems (such as children with Myers-Skelton Premature Immunosenescence), they attempted to control the infection and reshape the hosts into weapons. The result was a powerful and durable entity that could survive in hard vacuum, move at great speeds, and tear through hull plating and armored targets using its bare hands. When left to their own devices, the hybrids were attracted to and would chase after energy sources, such as radiation, to feed on them.
Although they successfully created an army of such hybrids in their research labs on the Jovian moon Io, they were unable to completely implement constraints for the protomolecule. As a failsafe, bombs were implanted in the hybrids' torsos, rigged to explode if the host was altered significantly after deployment. However, the oldest hybrids were eventually able to adapt to these bombs, expelling them from their bodies without setting them off, leaving them completely uncontrollable.
The hybrids are roughly humanoid, but the head is about twice as large as a human head and covered in protruding growths, and their hands are large and long. The skin is covered in black, chitinous scales, and the eyes glow with a bright blue light.