Hungarian and Viennese in origin, and named after Rigó Jancsi (1858-1927), a famous Hungarian Romani violinist. His good looks and fiddle so charmed the Belgian Princess de Caraman-Chimay (who was really Clara Ward, daughter of E.B. Ward of Detroit, the 'steamship king of the Great Lakes' who had made a name for herself striking artistic poses at the Folies Bergère in a flesh-coloured body stocking. Shirley MacLaine’s part in the film Can-Can was loosely based on her) that she left her husband, and ran off and married him. The newspapers at the time couldn't get enough of it.
The cake (it's uncertain with Rigó invented it or it was just named after him after he bought one) usually has a dense chocolate layer and a thin layer of apricot jam between the chocolate sponge, and is topped with a dark chocolate glaze.
Image by Antidiskriminator, Public Domain