arch-duke, n. — Green’s Dictionary of Slang

arch-duke n.

[? a specific archduke. DSUE suggests the Duke in Shakespeare’s Measure for Measure (1604), who is ‘certainly eccentric enough to serve as an archetype’]

a comical or eccentric person.

c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Archduke. an Eccentric or Comical fellow.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn).
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1859		Matsell Vocabulum 8: archduke. A funny fellow.