Chemo was originally a huge plastic vessel, about 25 feet tall and roughly man-shaped, built by eccentric scientist Doctor Ramsey Norton to contain the chemical by-products from his failed experiments to better motivate him to eventual success. Chemo grew into a building-sized giant and proceeded to kill Norton with a lethal dose of the growth-formula chemicals< He then went on a rampage, only to be defeated by the Metal Men.
Being a unique form of pseudo-life, Chemo could not really die. It returned time and time again, undergoing various resurrections and mutations, and had several more encounters with the Metal Men as well as squaring off against Superman.
Note:The Post-Crisis version of Chemo was involved in various groups, such as the Suicide Squad, Injustice League etc.