where was the enemy born?
Saturn's moon Titan
Thanos
Saturn's moon Titan 
who does thanos kill in infinity war comics Half of the living beings in the universe. what is the story behind this? It is about Thanos has collected all six Infinity Gems and attached them to his gauntlet. With their combined power, he becomes "like a god" and sets out to win the affection of Mistress Death, the living embodiment of death in the Marvel Universe. When Thanos uses his powers to instantly kill half of the living beings in the universe, Adam Warlock leads Earth's remaining heroes against him. where is the enemy's origin? He is a fictional character appearing in American comic books.
wiki:20145146
Thanos [SEP] Fictional character biography
Thanos was born on Saturn's moon Titan as the son of Eternals A'lars and Sui-San; his brother is Eros of Titan. Thanos carries the Deviants gene, and as such, shares the physical appearance of the Eternals' cousin race. Shocked by his appearance and the belief that he would destroy all life in the universe, Sui-San attempted to kill him, but she was stopped by A'lars. During his school years, Thanos was a pacifist and would only play with his brother Eros and pets. By adolescence, Thanos had become fascinated with nihilism and death, worshipping and eventually falling in love with the physical embodiment of death, Mistress Death.