thumb|Portrait, (engraved by [[Thomas Cross (engraver)|Thomas Cross)]]
John Heydon (10 September 1629 – c. 1667) was an English Neoplatonist occult philosopher, Rosicrucian, astrologer and attorney.
Life
Rosicrucian sources, including Heydon's own English Physician's Guide and Frederick Talbot's The Wise Man's Crown, give a florid biography for Heydon, including a claim to be descended from a King of Hungary. However, he was actually born in "Green Arbour" (near the Old Bailey), London, the son of Francis Heydon (of Sidmouth in Devonshire) and Mary (née Chandler, of Worcestershire). He was baptised at St. Sepulchre's Church. He had one sibling, a sister, Anne, two years his junior.
According to his own account, he was educated at Tardebigge, Worcestershire, among his mother's friends. He studied Latin and Greek with a tutor and was apprenticed to the study of law; however, his studies were interrupted by the outbreak of the English Civil War, and as a young man, he was said to have served in the royalist army. In 1651 he went abroad, travelling to Italy, Spain, Egypt, Arabia, and Persia.
On returning to England, he trained in law, and was articled as a clerk in 1652. In 1655, he was living in Clifford's Inn, practising as an attorney and also casting horoscopes. Heydon married the widow of Nicholas Culpeper in 1656, and is thought to have fathered a daughter. After 1658, he lived in "Spitalfields, near Bishopsgate, next to the "Red Lion".
In 1667, Heydon was imprisoned, again, in the Tower of London for his part in the treasonous plots of his patron, the Duke of Buckingham. He was accused of "treasonable practices in sowing sedition in the navy and engaging persons in a conspiracy to seize the Tower". He claimed however, that he was innocent and was the victim of someone paid to inform against him. He was referred to as "an ignoramus and a cheate" by Elias Ashmole; Frances Yates termed him a "strange character...an astrologer, geomancer, alchemist, of a most extreme type."; while A. E. Waite considered that all that was of value in his mysticism was derived from anterior writers.