Who discovered tea as a beverage?

"Tea", can be basically described as an infusion herbs in boiling water, so the practice of extracting the "medicinal" components of herbs has been with mankind since before written record.

The beverage we have commonly come to call "tea" is the result of steeping the leaves of the tea tree (Camelia sinensis) in boiling water. There is a written record by Lu Yu, from 780 AD, the Ch'a Ching (Tea Classic). This however, is a scholarly work about the many teas favoured in China at the time, suggesting that tea had been an accepted beverage for unknown generations before that.