Thanos was one of the last sons of Alars, progenitor of the second colony of Eternals of Titan, and Sui-San, the last survivor of the original settlement of Eternals on Titan. Born with grey, hide-like skin and a massive body, Thanos was a morose child who became obsessed with the concept of death. Through bionic implementation and long hours of meditation, Thanos augmented his Eternal strength and powers to that his powers surpassed those of all other Titanian Eternals. As he grew in power, Thanos also grew in ambition and desire for conquest. Thanos stole one of his people's starships and traveled to other star systems to recruit soldiers, mercenaries, and malcontents for a private army. With a small fleet he dropped nuclear devices on his home world Titan, killing thousands of his people, including his mother Sui-San. Declaring himself ruler of Titan, he then set his sights on Earth.