Thanos, also known as the "Mad Titan", is one of the most powerful, insane and evil of all villains in the Marvel universe, created by Jim Starlin and debuting in 1973 in an issue of Iron Man and continuing to terrorize the entire Marvel universe and beyond up to the modern era. His popularity as a supervillain is seen in his ability to hold a large presence both in mainstream Marvel comics and his own series while also being seen in a large array of products ranging from videogames to toys and cartoons (though his nature is toned down in some of the cartoons, for obvious reasons).
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Thanos, referred to as the Dark Lord by his most loyal underlings and the Mad Titan by the galactic community, is a powerful, cosmic warlord who rules over a distant region of space and also commands two massive armies known as the Chitauri and the Outriders. His own main objective is to obtain the Infinity Stones, and his desire to achieve this goal is what led him to forging deals with Loki and Ronan the Accuser in their respective campaigns against Earth and Xandar, promising to aid them in exchange for an Infinity Stone. Both of these new alliances cost Thanos much of his resources, including one of the stones and the loyalty of his two daughters, Gamora and Nebula, and inadvertently resulted in the formation of the two superhero groups: the Avengers and the Guardians of the Galaxy. Fed up with these failures of his servants and opted to seek out the Infinity Stones himself.
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Virtual Immortality
Regeneration
Super Strength
Flight
Teleportation
Matter Manipulation
Telepathy
Illusion Casting
Mind Control
Cosmic Power
Generation of energies that his body consists of(cosmic, force, light, heat and other forms of electromagnetic radiation)
On top of that, Thanos also knows magic and incorporates technology in his abilities. He told Gamora he started dabbling in the occult 300 years before she was born implying he has several hundred years of experience using magic. It's also been stated that he has spent centuries enhancing his power with both magic and technology(bioenhancements), and his power increased 10 fold after Death resurrected him making him a lot more powerful than a typical Eternal.
Other powers and abilities Thanos has shown not listed above for Eternals.
Super Intelligence(His greatest weapon and even he says this himself)
Teleportation via technology
Barriers via technology
Force Fields via technology
Magic
Super Durability/Invulnerability
Energy absorption
Resistance to psychic powers/telepathy(mind control and mind reading etc...)
Resistance to reality warping
Resistance to cosmic awareness
Cosmic spanning senses(Gained after Death resurrected him)
Can heal himself and other people
Can give powers to other people
Thanos is also a genius in technology and science. He has traveled throughout the cosmos learning technology from different civilizations and planets. He can create advanced technology beyond the technology you'd typically see on Earth. Some of the notable stuff Thanos has created includes...
Chair that can teleport, levitate and withstand a fully powered cosmic bolt attack from Silver Surfer
Time machine that can travel through time and probe past and future events
Artificial black hole
Ion laser projector
Inter-dimensional communication implant
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