Rigdum Funnidos is a character in Henry Carey's Chrononhotonthologos (1734).
Rigdum Funnidos is the comically plain-spoken contrast to the bombastic Aldiborontiphoscophornio.
Both are courtiers, but whereas Aldiborontiphoscophornio might explain, when asked who Somnus is, Rigdum Funnidos responds, Rigdum is both a Sancho Panza to the absurd Aldiborontiphoscophornio and a figure of the "Plain Dealer" (see The Plain Dealer by William Wycherly).
It is also Sir Walter Scott's nickname for John Ballantyne.
Conversely Aldiborontiphoscophornio was Scott's name for James Ballantyne in allusion to his pompous manner.