Subject One was a genetically modified Spaghetti Person.
History[]
Morty wanted to stop the slaughter of Spaghetti People, but had to do so in a way that didn’t stop the production of suicide spaghetti. One of Morty’s ideas was to make "less humane” clones of Spaghetti People. Rick approved of the idea.
In a laboratory, Rick created a genetically modified spaghetti person, whom he called “Subject One”. The subject had the same physiology as a normal person, but with no frontal lobe or empathy centers. However, for that person there was no difference between being alive or dead, so he couldn't generate spaghetti.
It’s unknown what happened to Subject One afterwards.