They were ordinary employees at RX Tech working for Mark Willard in Antarctica who was trying to find the location of a mysterious meteorite that had been made into four strange artefacts called the Infada Stone, Ora Dagger, Element 115 and The Eye of Isis.
He found the crater where the meteorite struck hundreds of years ago and began making experiments into the area's propensity for rapidly spurring on the process of evolution, using some of his employees as guinea pigs for his schemes. Instead of evolving however, they ended up turning into mutants. It made some of them lose their legs and become seal like creatures that breathed poison, while others morphed into creatures with warped heads, hoofed feet and claw-like appendages that could rip things apart. Both were hideously deformed and devoid of humanity in appearance and demeanour, leaving them as little more than mindless, homicidal drones.
These lesser mutants can be seen as the precursor to Willard's much more powerful and self-aware/intelligent form, for instance in the head of the torso mutants.
On travelling to Antarctica, archeologist Lara Croft, who had been hired by Dr. Willard to find four Meteorite Artefacts stolen from the area, discovered one of his mutated employees, who was probably the first of the mad scientist's creations. She later went to see Dr. Willard to give him the artifacts, where he told her that the power of them can change everyone into powerful mutants.
Lara is horrified and tries to stop him, but he betrays her and escapes with the artefacts to the Meteorite Cavern in the excavation site. Lara follows him to the mines where many more of Willard's hideous creations awaited her. She killed every single one and the deadlier Tinnos Mutants until she finally found Willard in the cavern itself. He uses the combination of the four artifacts to unlock the meteorite's core and become the deadliest mutant of all, but Lara defeats him by removing the artefacts and thus the meteroite's power to protect him, leaving the deranged scientist's work in ruins.