(Capcom's primary storyline)
Operation: Emperor's Mushroom was an operation conducted by the Umbrella Biohazard Countermeasure Service, under the direct supervision of Nikolai Zinoviev. It was conducted on the grounds of Raccoon University.
That part, at least, went as planned. The team engaged Thanatos in the University's Back Square and allowed Nikolai to plant an extractor on its back, draining an amount of its blood into a capsule.
At that point, though, things got out of control. Thanatos slaughtered the ground team and escaped before the blood sample could be retrieved.
The operation was a failure. The blood sample was taken by survivors and used to synthesize the Daylight vaccine. Nikolai destroyed the main building of the university as ordered, and all evidence of the mission was wiped out in the missile strike that consumed the city.
Emperor's Mushroom is the English name for Amanita caesarea, literally "Caesar's mushroom". The fungus was a notable delicacy among the ruling families of Rome. Agrippina the Younger most famously prepared a dish of Amanita caesarea with Amanita phalloides, a poisonous member of the same genus, to kill the emperor Claudius. Claudius's death assured the succession of Agrippina's son Nero (Tacitus, Annals, book XII).