And if you weren't RoboSam, you'd feel it, too.
Let me get dressed, Robocop.
– Dean Winchester, 6.08 All Dogs Go to Heaven
"RoboSam" is a term fans and reviewers use to describe Sam in early season six when he is saved from Lucifer's Cage without his soul. Robocop was the main character in a movie of the same name about a cop who is wounded and then made into a powerful cyborg. Dean also referred to Sam as a replicant in 6.10 Caged Heat, a reference to the cybernetic humans from the movie Blade Runner. Other terms used are Soulless!Sam or Not!Sam. General fandom consensus was that RoboSam was very hot and the most badass Sam has ever been.
When Sam came back from Hell his soul was left behind which left him completely emotionless. He has said himself that he doesn't feel anything anymore, with no remorse. The new Sam will do anything to kill monsters, even let his own brother be turned into a vampire. Sam claims that it has a few benefits that have allowed him to become a better hunter: he doesn't need to sleep or really eat anymore, he has a higher pain tolerance and was able to lie to the goddess Veritas, even though she can make all other people, even Dean, tell the truth. This soulless version of Sam has also been proved to be quite dangerous, with his lack of emotion or empathy for others makes him something of a sociopath. He doesn't seem to care about those he works with, or even his brother Dean, as he just uses those close to him to achieve his own ends. This comes to a head by the middle of season six, when Death restores Sam's soul. His next appearances were in flashbacks in 6.13 Unforgiven and in the season finale 6.22 The Man Who Knew Too Much in Sam's head.
In 9.17 Mother's Little Helper, the case Sam is investigating in which people are becoming violent and impulsive, reminds him of his year being soulless.