Yngvi
from Fancyclopedia 2 ca. 1959
(De Camp&Pratt) The only thing we are told about Yngvi is that when Harold Shea and Asa-Heimdall were in the dungeons of the Fire Giants in "The Roaring Trumpet", a little fellow came to the front of his cell every hour on the hour and yelled "Yngvi is a LOUSE!" The mystery has fascinated fandom, and Yngvi has turned up in all sorts of places — a statement as true today as when Speer wrote it fifteen years ago. Sometimes the statement that he is a louse is taken literally; sometimes Yngvi is confused with the little guy who didn't like him; once it was said that Yngvi is a Type Fifteen fan. Elmer Perdue defended him/it gallantly during Third Fandom days, asserting by sticker and otherwise that "Yngvi is NOT a louse!" At the DenVention, Rothman made a motion to the effect that Yngvi is not a louse, but it was defeated. A motion was then passed that Rothman is a louse. The matter was brought up again at the 1950 PhilCo but ruled out of order by Moskowitz, who misremembered that Rothman's motion had carried. In 1958 Sandy Sanderson used "Yngvi" as ekename for a fan who'd been sending postcards to insurance companies advising them that Inchmeryites were good prospects, and getting salesmen to call.

Research by your J Fiske turns up the fact that in Scandinavian legend (the background-mythos for "The Roaring Trumpet") the primordial gods Odin, Vili and Ve were the progenitors of (respectively) the Norse, German, and English races, and "Ing" or "Yng" means roughly "the people of __". Somebody like Col McCormick or another of the rabid English-haters who at the time TRT was written were making all possible capital out of the freshly-begun Second World War may have been the original of the little man in the phrase.
from Fancyclopedia 1 ca. 1944
(de Camp) - The only thing we are told about Yngvi is that a little fellow in the Giant's prison of "The Roaring Trumpet" came to the front of his cell every hour on the hour and yelled "Yngvi is a LOUSE!" The mystery has fascinated fandom, and Yngvi turns up in all sorts of places. Frequently the statement that he is a louse is taken literally; sometimes Yngvi is confused with the little guy who didn't like him; and once it was said that Yngvi is a Type Fifteen fan. Elmer Perdue has been the leading defender of him or it, asserting by stickers and otherwise that "Yngvi is NOT a louse!" At the Denvention, Rothman made a motion to the effect that Yngvi is not a louse, but it was defeated. A motion was then passed stating that Rothman is a louse.

At the 2012 Worldcon, Chicon 7, a motion was made at the WSFS Business meeting that "Yngvi is not a louse". The p/e/r/p/e/t/r/a/t/o/r/s/ makers of the motion even conducted a small-scale campaign including ribbons and bookmarks. In spite of that, the business meeting voted decisively against the motion, leaving poor Yngvi still a louse. Ribbons also appeared designating Deb Geisler, Michael Benveniste, and Geri Sullivan, the makers of the motion, as lice, although no motion making that claim was made.

T.K.F. Weisskopf has published a fanzine titled Yngvi is a Louse.