Who was the letter sent to in the gunpowder plot?

The letter in the Gunpowder Plot, specifically known as the "Monteagle Letter," was sent to William Parker, the 4th Baron Monteagle. The letter warned him to stay away from Parliament on the opening day, suggesting that a plot was afoot to destroy the building. This warning ultimately led to the discovery of the Gunpowder Plot, where conspirators planned to assassinate King James I and blow up the Houses of Parliament in 1605.