Thomas Phelippes (1556–1625) was a forger and intelligence gatherer. He served mainly under Sir Francis Walsingham, in the reign of Queeen Elizabeth I, deciphering the codes of those plotting against her. He is most remembered for his adding of a postscript to the "bloody letter" sent by Mary Queen of Scots to Anthony Babington regarding the Babington plot. This postscript asked Babington for the names of the plotters involved in the planned assassination of Elizabeth and hence Walsingham was able to "prove" Mary's direct involvement in the plot, and have her executed.