Which lord received the anonymous letter warning of the Gunpowder Plot?

The lord who received the anonymous warning about the Gunpowder Plot was Lord Monteagle, formally William Parker, 4th Baron Monteagle.

On 26 October 1605, while Parker was at his house in Hoxton, London, a servant delivered a mysterious letter from an unidentified writer. It warned him to avoid the opening of Parliament because the assembled lawmakers would receive a “terrible blow.” The message did not name the conspirators or explain the planned explosion.

Monteagle promptly showed the letter to Robert Cecil, Earl of Salisbury, who passed the warning into the government’s hands. The king’s advisers eventually ordered a search beneath the House of Lords. On the night of 4 November, guards found Guy Fawkes with matches and discovered barrels of gunpowder hidden under coal.

The letter’s authorship remains debated. Francis Tresham, Monteagle’s Catholic brother-in-law, has often been suspected, but the evidence is inconclusive. Monteagle was rewarded with money and land for helping expose the conspiracy.