Thomas Howard, 5th Duke of Norfolk (9 March 1627 – 13 December 1677) was an English nobleman who from 1645 was deemed a lunatic.

Unable to coherently manage his English estates, the running of them was given over to his next eldest brother, Henry Howard, who acted in his place.

In 1660 Henry successfully petitioned the House of Lords to have the attaindered title Duke of Norfolk restored.

It was suggested that Henry was holding Howard at Padua in bad faith in order to reap the benefits of representing him in England.

In 1641 the English Civil War was brewing and he left the country with his grandfather Thomas Howard, 14th Earl of Arundel.

[7] Howard's grandfather, who was created Earl of Norfolk in 1644, never returned to England, dying at his villa in Padua on 4 October 1646.

[9] His father spent the rest of his life refusing to consent to the 14th Earl's will, which left most revenues to his widow Alethea Howard, Countess of Arundel, and attempting to overturn it.

Having travelled from Utrecht to visit his family in Padua in 1645, Howard fell ill there with a fever that caused him brain damage, leaving him "to sink into irredeemable lunacy" according to the biographer John Martin Robinson.

[15][16] Howard never left Padua, being cared for by Henry Yerbury, an English physician, and his household controlled by a local Italian, Carlo Theobaldi.

[12] The man who inherited his father's honours in 1652 was described by a visiting Sir John Reresby as showing:"all the Symptoms of Lunacy and Distraction"[17] Being both abroad and insane, Howard was unable to manage his English estates.

When this situation first came about, rumours were spread that Howard was being kept against his will in Padua so that Henry could take advantage of the powerful position left in his absence.

[12] The family monitored Howard and his condition, ensuring that he had no opportunity to marry whilst insane so that his malady could not be passed on.

The Commons denied these petitions, choosing to believe the testimony of visitors like Reresby and in fear of what allowing such an important but insane man into the country might result in.