"Invented" isn't what Moke123 said. "Became commercially available" means that someone came up with a viable bulk-chemical manufacturing process to provide a reasonable yield of the synthesis of the drug.
The drug was first synthesized in a lab in 1877 by H. N. Morse. It was first used medicinally in 1893 by J. von Meering, originally described using the name 'paracetamol' - which is quite normal. Chemicals have "common" names assigned by their discoverers, IUPAC names, and often, trade names. "Tylenol" is a trade name, a brand name of sorts. Acetaminophen is a common name. In the UK, it is still known as 'paracetamol.'
As is common for complex compounds, it has multiple formal names.
4-hydroxyacetanilide - formal name based on being a derivative of acetanilide
4-Acetamidophenol - formal name based on being a derivative of phenol
N-(4-hydroxyphenyl)acetamide - preferred name under the naming rules of the International Union of Pure and Applied Chemistry (IUPAC).
In the 1950's, B. Brodie and J. Axelrod rediscovered it as a preferable substitute to other analgesics at the time that had higher liver toxicity side-effects. Aspirin helps with pain but has side-effects with blood clotting factors. Morphine derivatives help with pain but are addictive and affect respiration. Naproxen sodium and Ibuprofen have worse levels of liver effects. The search for a good pain-killer in the 1950s led to the rediscovery of acetaminophen as having the least (though still not zero) liver toxicity.
By 1955, McNeil Labs introduced it as Elixer Tylenol. It is this latter fact to which Moke123 must have referred.