Was chlorine discovered or invented?

Chlorine was discovered by Carl W. Scheele (1742-1786) in 1774 but it was not yet known as an element. Due to its strong oxidising properties it was thought by most chemists to contain oxygen and was called oxymuriatic acid (muriatic acid being HCl or hydrochloric acid).
More information about C. W. Scheele on chemistryexplained.com

It was Humphry Davy (1778-1829) who exposed the gas to white-hot carbon in an attempt to remove the oxygen as carbon dioxide. He was never able to produce oxygen or any compound known to contain oxygen, and he finally concluded that chlorine had to be an element. Because of its greenish yellow colour, he called it "chlorine" after the Greek "chloros" meaning yellow-green.