Sasori was once part of the Hidden Sand Village, but 20 years ago he left the village and became a missing-nin. He develops and uses many battle puppets to fight his opponents with. Even Karusu, Kuroari, and Sanshouuo, the puppets that Kankuro, uses were made by Sasori.
He is a very skilled ninja, with many aces up his sleeve. He is part of Akatsuki and travels around with Deidara as his Akatsuki partner. Before Orochimaru left Akatsuki and Deidara became Sasori's partner it was Orochimaru who was part of a team with Sasori. Sasori is also known as "Akasun no Sasori" or "the Scorpion of the Red Sand". He is very impatient and likes to get things done as fast as he can, he doesn't like to let people wait or be waiting himself.
Sasori lost his parents at a young age and was left in the care of his grandmother, Chiyo. It's her who taught him everything there is to know about puppetry. When Sasori first learned how to use this ability, he made puppets resembling his dead parents in order to feel loved by them. He later on starts creating human puppets (puppets made from human bodies) from opponents he thought worthy of becoming his puppet.
His favorite puppets are Hiruko and the Third Kazekage, both shinobi from the Hidden Sand who he kidnapped and killed to become part of his collection. Hiruko is a more defensive puppet, while through the Third Kazekage's puppet Sasori can use the Third's unique Iron Sand ability.
But that's not all, Sasori himself is actually a puppet too, he converted his own body into a puppet. It gives him a young appearance, and let's him control 100 puppets at once by using a mechanism on his chest that can spin numerous chakra strings. To be able to do this he has to be able to use chakra, for this reason his heart is preserved inside his puppet. His heart, being the only part left of his human body, is the only way to really kill Sasori. Otherwise he'll just transfer his heart to another puppet.
Sasori is eventually killed by his grandmother Chiyo and Sakura. He is stabbed through the heart in the form of a hug by the human puppets of Sasori's parents. After his defeat Sasori informs Sakura of his spy within Orochimaru's ranks, Yakushi Kabuto. He tells her where and when she can meet him.