Henry Percy, ninth Earl of Northumberland, was born in 1564. The Percy’s were a very powerful noble family with very large estates in Yorkshire, Northumberland and Cumberland with others scattered all throughout England and Wales. Their allegiance to Catholicism had made them outstandingly dangerous to the government of Elizabeth I. The seventh Earl was executed in 1572 for his part in a revolt in 1570; his heir, the eighth Earl died in the Tower of London in 1585, where he was being held under suspicion of being involved in another plot to free Mary Queen of Scots from imprisonment at the hands of Elizabeth I.
The ninth Earl was brought up a Protestant but was more interested in science and “magic” than in religion - he was often referred to as the 'Wizard Earl'. He did, however, show enough interest in the troubles of the English Catholics to attempt to debate their position with King James of Scotland before he ever came to the throne of England. He picked Thomas Percy - his cousin and senior manager of his many estates - to speak on his behalf. After James's accession to the throne, the King made the Earl of Northumberland the captain of his royal bodyguard and granted him membership of the Privy Council, regardless of this Northumberland continued to act as champion for the English Catholics.
When the Plot was uncovered, Thomas Percy's involvement was seen by the government to indicate that Northumberland had something to do with it as well. They concluded that the plotters must have a nobleman in mind to lead the country if the Plot had succeeded and found it difficult to believe that Thomas Percy would have let Northumberland die in the attack on the House of Lords.
Northumberland was taken into custody and put in the Tower of London on 27th November. He was not tried until much later, on 27th June 1606, when he was stripped of his public offices, fined £30,000 and sentenced to imprisonment at the King's pleasure. In the Tower he remained until 1621, where he was treated well and lived comfortably. He died in 1632.
William Parker, better known as Baron Monteagle was born around 1575 and raised as a Catholic. He was intimately involved with radical plans for the Spanish military to intervene in support of the English Catholics during Elizabeth’s reign.
He was married to Francis Tresham's sister, and knew Thomas Winter well. He was also linked to Essex's rebellion in 1601. Despite being imprisoned and fined for this involvement he was still a part of the plan of Spanish intervention in 1602, but when James came to power he swore to him that he was no longer concerned in plots.
Baron Monteagle received the 'Monteagle Letter' on 26th October. He was present during the first search of the House of Lords cellar on 4th November. For his quick thinking and swift action, Monteagle was rewarded with lands and an annual pension, although it does appear that he was still treated with suspicion by the government. He died much later, in 1622.