He became a friend of Morty, who wanted to save his life from Michael, the alien assassin, yet, it was all just a cover following the reason that Fart wanted to bring his species, and to cleanse the universe from many life forms based on carbon, for which they see them all as a "illness".
Fart was a life form from another dimension that was being held captive and ordered to be assassinated by Krombopulos Michael. With the ability to alter the composition of atoms, Fart could produce any element from any atom by adding or removing protons, making him incredibly valuable to anyone who captured him.
Following an argument with Rick, who sold weapons to Fart's soon-to-be assassin, Morty set off to rescue Fart in an attempt to make a positive difference by saving its life. However, in the resulting pursuit, hundreds, if not thousands, of police and civilians died.
Just before Fart enters a wormhole that would return him home, he reveals to Morty that he plans to come back with many more of his kind on a mission to destroy carbon-based life, which he views as a disease. After this is revealed, Morty kills Fart.
Krombopulos Michael states that Fart "can't be killed with regular matter" when he purchases an anti-matter gun from Rick. Morty uses the weapon to kill Fart.
Fart was a light neon blue colored cloud of translucent gas. It had five electric orbs inside of it that are the colors purple, pink, green, blue, and orange. Each one glows for every syllable he would speak.
Fart was a very calm and emotionless being who did not take anything too seriously. Fart was also very polite, thanking and complimenting people he interacted with a lot. It saw the true beauty in the universe. Fart looked down upon carbon-based life, considering them to be a "disease" that needed to be eradicated.
It made exceptions from it's views though, as it considered Morty to be different and understanding, though it likely wasn't going to spare Morty's life.
Fart was not referred to as a hero, but it was an anti-heroic villain, intent on accomplishing his goal to cleanse the carbon-based life from the universe.
- The 'visions' caused by Fart are largely inspired and an homage to the works of Vince Collins (especially 'Malice in Wonderland'), american filmmaker and animator active in the psychedelic movement. https://youtu.be/R2BAeh8wZLI https://youtu.be/8OHnC24Qx8k
- The portal to the dimension in which Fart comes from is in the shape of a vagina, implying that Fart is actually some kind of an interdimensional queef.