Thanos, one of Marvel Comics' most formidable villains, is a character of immense complexity and depth. Created by writer-artist Jim Starlin, he first appeared in "The Invincible Iron Man" #55 in 1973. Thanos' story is a blend of cosmic power, philosophical motivations, and a tragic background that defines his path as a conqueror and destroyer.

### Origin and Background
Thanos was born on Titan, one of Saturn's moons, to the Eternals A'Lars (also known as Mentor) and Sui-San. Unlike his fellow Eternals, who appeared human, Thanos was born with the Deviant gene, giving him a hideous, monstrous appearance. This caused him to be shunned by his peers and even his own mother, who was driven mad by his appearance and tried to kill him at birth.

Growing up in isolation, Thanos became obsessed with the concept of death. He was a brilliant student, excelling in science and philosophy, but his interests took a dark turn. Thanos began conducting dangerous experiments, delving into forbidden knowledge, and ultimately becoming fascinated with nihilism and the personification of Death in the Marvel Universe, Mistress Death.

### Transformation into Thanos
Thanos' transformation from a curious, ostracized child to the Mad Titan was gradual and rooted in his obsession with death. As he grew older, his fascination with Mistress Death intensified. He sought her approval and love, believing that to gain her affection, he needed to prove his worth through acts of mass destruction and genocide.

Driven by this twisted love, Thanos embarked on a journey of conquest, gathering immense power and resources. He enhanced his physical abilities and intellect through bionic and mystical means, making him one of the most powerful beings in the universe. He amassed a fleet of loyal followers, known as the Chitauri and other interstellar armies, and began his quest to achieve ultimate power.

### Quest for the Infinity Stones
Thanos' most significant and well-known pursuit was his quest to gather the Infinity Stones, six powerful gems that, when combined, grant the user god-like control over the universe. These stones represented different aspects of existence: Space, Time, Reality, Power, Mind, and Soul. Thanos believed that by wielding all six stones in the Infinity Gauntlet, he could achieve his ultimate goal: to wipe out half of all life in the universe, thus impressing Mistress Death with the scale of his devotion and destruction.

### The Snap and Its Aftermath
Thanos' quest culminated in the events of "Infinity Gauntlet" in the comics and the "Avengers: Infinity War" and "Avengers: Endgame" movies. He succeeded in assembling the Infinity Gauntlet and, with a snap of his fingers, eradicated half of all life in the universe. This event, known as "The Snap," had profound implications for the surviving heroes and the entire cosmos.