Gérard I is a proposed Count of Loon, in what is now Belgian Limburg, who was mentioned in a 1101 charter of Emperor Henry IV concerning the return of the town of Andenne by Albert III, Count of Namur. He probably did not exist.
The charter, or at least one version of it, mentions a list of people including "Gerardus Comes de Looz, Arnoldus et frater ejus Theodoricus, Gislebertus filius Comitis Ottonis, Comitis de Duras" meaning Gerard is specifically a count of Looz or Loon, whereas Arnold, mentioned next (with his known relatives Theoderic, Gislebert, and Otto) would have been expected from other records.
In an 1866 article on Arnold I, Count of Looz in the Belgian National Biography, Jean-Joseph Thonissen concluded that he died between 1098 and 1101, succeeded by his eldest son Gérard, followed by his younger son Arnold II. But these conclusions are not generally believed, and current historians agree on 1126 as the correct date of the death of Arnold I, with his son Arnold II succeeding him directly.
It was pointed out by J. Daris in 1867 that there was another copy of the charter of 1101 which called Gérard simply a count, and Arnold was the one described as "Comes de Looz".
The charter involved appears here.