The discovery of marijuana cannot be attributed to a single individual as it has been used by humans for thousands of years. However, key figures in its study include:

• The earliest known medicinal use of cannabis dates back to ancient China around 2700 BCE, attributed to the mythical Emperor Shen Nung, who is said to have discovered its healing properties.

• Cannabis evolved in Central Asia and was used as medicine in Asia around 500 BCE.

• In the 1830s, Irish doctor William Brooke O'Shaughnessy introduced cannabis to Western medicine through his observations and medical use of the plant in India.

• Raphael Mechoulam, an Israeli researcher, discovered tetrahydrocannabinol (THC), the primary psychoactive compound of cannabis, in 1964, earning him the title "father of cannabis research".

Thus, marijuana was first discovered and used by ancient civilizations for medicinal and ritual purposes, with scientific understanding significantly advanced by researchers like O'Shaughnessy and Mechoulam.