The King of the Silver Lands is never explicitly named in the comic, but it is strongly implied that he is the in-comic version of Cheyenne Wright. While Cheyenne's fictional alter ego has never appeared in the comic proper before, he has appeared, under his own name, in many presumably non-canonical
As the King of the Silver Lands, he is ruler of the Argurons, a technically-secret civilization living deep beneath Paris. When by Agatha and Co. that much of his court has been infested with Revenants, he proclaims that he was already well aware of this fact, and that he serves a "glorious Queen", presumably referring to some version of The Other. Whether he himself is a revenant (or a Spark) has not been made entirely clear; either way, he displays a great deal of hammy enthusiasm for the idea.
Following a failed attempt to capture Agatha and her companions, he becomes the target of a successful kidnapping plot by Boris, Jenka and his own daughter Larana, and is taken as a unconscious prisoner to the nearby Immortal Library of the Grand Architect.
Unfortunately, while Agatha and her companions are searching through the Library's sealed Corbettite Vaults, he is nearly able to of the Library with the help of Slaver Wasps as supplied by a Geisterdame ally who might be Madame Velix. However, this attempt is thwarted, and he is officially overthrown by Larana.
It is then revealed that he was (and still is) a professor of color theory at Transylvania Polygnostic University who "went rogue" twenty years ago while on a research trip, and married Larana's late mother. (It's an old, old story.) He is to be taken back to TPU to face the Board of Regents in regards to certain irregularities in his grant expenditures, a fate which perhaps even he does not deserve.
Outside Information Edit
Because his daughter's name is Larana Chroma, it seems reasonable to assume the King's own surname is also Chroma. Since Cheyenne is the colorist for Girl Genius, this would seem to be something of an inside joke.