Porteus Knatchbull was the ninth Minister for Magic, in office from 1781 to 1789 (Pm).
When King George III was thought to be losing his mind, the Muggle Minister at the time, Lord North, asked Knatchbull for help with his condition (Pm). Unfortunately this backfired on Lord North as soon as his constituents found out he believed in Wizards, and he got the boot.
Asked to help diagnose the illness of the Muggle King George III, perhaps to heal him using potions.
King George III of England reigned during the Revolutionary War and his "madness" is sometimes thought to be the reason the British lost the American colonies. The King suffered from several strange symptoms: drooling, confusion and convulsions. Some historians believe he had dementia, while others believe it was manic depression. His urine was blue, which is a symptom of the illness porphyria (which also causes madness), but some say he was given the plant gentian as a tonic and perhaps that blue flower turned his urine blue, or was even responsible for his other symptoms. (Whether he got the potion from Wizards or not, there is no canon.)
Lord North, the Muggle Prime Minister under King George III, was the first to ever receive a vote of no confidence after British forces lost the Battle of Yorktown to the colonists during the Revolutionary War for Independence. He left office in 1782, so Minister for Magic Porteus Knatchbull outlasted him by six years.