Short answers, pulled from the story.
The first adult animated series to air on American television premiered in 1993 with the show Beavis and Butt-Do. This series shattered the unspoken rule that animation was exclusively for children and aired for only six episodes.
The Simpsons premiered on the 24th of May 1989 and was created by Matt Groening and James L. Brooks. It became the longest-running American scripted primetime television series in history.
South Park premiered on the 13th of August 1997 and was created by Trey Parker and Matt Stone. The show became the most controversial and influential adult animated series of the late 20th century.
Futurama premiered in 1999 and was created by Matt Groening. The show explored themes like time travel, artificial intelligence, and the nature of consciousness.
The first adult animated series produced in Japan premiered on the 15th of June 2005 and was titled FLCL. The show was created by Kazuya Tsurumaki and combined adult themes with a unique animation style.