Robert Wintour and Thomas Wintour, also spelt Winter, were members of the Gunpowder Plot, a failed conspiracy to assassinate King James I. Brothers, they were related to other conspirators, such as their cousin, Robert Catesby, and a half-brother, John Wintour, also joined them following the plot's failure. Thomas was an intelligent and educated man, fluent in several languages and trained as a lawyer, but chose instead to become a soldier, fighting for England in the Low Countries, France, and possibly in Central Europe. By 1600, however, he changed his mind and became a fervent Catholic. On several occasions he travelled to the continent and entreated Spain on behalf of England's oppressed Catholics, and suggested that with Spanish support a Catholic rebellion was likely.

The Gunpowder Plot of 1605, in earlier centuries often called the Gunpowder Treason Plot or the Jesuit Treason, was an unsuccessful attempted regicide against King James I by a group of English Catholics led by Robert Catesby who considered their actions attempted tyrannicide and who sought regime change in England after decades of religious persecution.