Tylenol was invented by Robert L. McNeil Jr., who was a chemist and the grandson of Robert McNeil, the founder of McNeil Laboratories [3]. McNeil Laboratories was established in 1879, and it was initially a drug wholesaler [3]. In 1955, Robert L. McNeil Jr. developed Tylenol, which was initially marketed as a prescription drug for pain relief and fever reduction [2]. However, in 1960, Tylenol became available over-the-counter [2]. McNeil Laboratories was acquired by Johnson & Johnson in 1959, and the company continued to produce and market Tylenol [2]. Tylenol became a popular pain reliever, and it remains one of the most widely used over-the-counter medications in the world [1].

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/TYLENOL
[2] https://www.nytimes.com/2010/06/04/business/04mcneil.html
[3] https://en.wikipedia.org/wiki/Robert_L._McNeil_Jr.