"The Clone" is the name given to the amorphous flesh monster in Theodore L. Thomas and Kate Wilhelm's science fiction novel The Clone, adapted from Thomas' short story of the same name. The name is slightly misleading, as the creature isn't a clone of anything, nor does it clone itself. It is accidentally created when some pollutants and chemicals mix with meat particles in a sewer catch basin in Chicago. Beginning as a single-celled organism, the "clone" soon grows into an enormous bloblike creature that fills the sewers under Chicago, eventually flowing up through pipes and drains, where it begins attacking humans, causing a citywide crisis.
When first created, it was colorless, but upon first emerging from the sewers and being touched by the sun, its skin turns green. Having meat in its genetic makeup, it is flesh more than slime, but extraordinarily amorphous, capable of flattening or stretching itself into different shapes to suit its environment, such as spreading itself out flat to cover walls and floors, and it can also sprout tentacle-like tendrils to seek out food. Its "food" is basically anything it can get ahold of, people and animals in particular, but it'll also consume inorganic materials as well. It enjoys some synthetic fabrics like polyester and the rubber of car tires, as well as some minerals making up concrete; by the time it grows so huge it fills the entire city, it causes buildings to collapse by leeching minerals from the concrete in them, weakening their foundations.
As opposed to digesting its victims, it directly converts whatever it touches and desires to add to its own mass into its own tissue. If a human victim's bare hand touches the clone's flesh, the hand simple "melts" into the surface of the clone's mass; the hand, skin, bones, muscle and all, has ceased to exist, converted directly into clone tissue, with the now unfortunate human victim stuck to the creature, existing as a living extension of it - until the absorption process creeps up the arm and reaches the heart or the brain or another vital organ, whereupon the person will instantaneously die. The only mercy is that the process is entirely painless, with many people not even realizing they've touched the clone and are being converted until it is too late.
The only way to save a person who has had one of their non-vital limbs grabbed by the clone is to amputate the limb or pour iodine on it, as iodine is the only thing capable of harming the creature, since it causes the tissue to shrivel up and die. The person who had their arm amputated survived, while the person who had iodine poured on their partially-converted hand did not, because the iodine only killed the surface tissue; the clone flesh underneath the dead surface then went into the man's arm under the skin and absorbed him from the inside-out. No one, not even the victim, realized anything was wrong until he suddenly dropped dead when the conversion process reached his heart.
The clone was killed when the National Guard and Chicago Fire Department sprayed a perimeter of iodine around the city and also sealed off all the sewer exits and prevents the creature from getting into Lake Michigan, trapping it in the city. After failing to find any remaining nutrients to convert, it turned to converting its own tissue, eating parts of itself in a citywide orgy of cannibalization, until it broke down on a cellular level and finally died from a mixture of molecular instability and starvation, collapsing into several thousands or perhaps millions of pounds of lifeless mush.