Francis Tresham was born around 1567. He was the eldest son of the eccentric and formidable Sir Thomas Tresham, a Catholic, who lived at Rushton Hall in Northamptonshire and designed a pair of extraordinary buildings - which still exist - exploring Catholic symbolism.
Tresham was a cousin of Robert Catesby, and friendly with the Wright brothers. Like them, he was involved in the 1601 rebellion of the Earl of Essex against the dominance of Robert Cecil, Queen Elizabeth's chief advisor.
When that failed Tresham was imprisoned and fined, but still involved himself in secret discussions with the Spanish court in 1602 and 1603.
Catesby and the other conspirators didn't let Tresham into the secret of the plot until very late - in October 1605 – since they were worried he wasn't completely trustworthy.
Because his father had recently died, Catesby and the rest believed that Tresham now had access to a lot of money. But the latter seems to have been appalled by the conspiracy, and certainly claimed later that he tried to stop the plot and was planning to leave the country.
Tresham was probably the writer of the Monteagle Letter warning his brother-in-law, Lord Monteagle, not to attend Parliament on the 5 November, although he denied it when challenged by the conspirators on 1 November.
After the discovery of the plot, he feigned complete innocence, but was named by Guy Fawkes and arrested on 12 November. He died in the Tower on 23 December 1605 of a natural illness.