Kingdom of León
This is a mod created by Moltke that featured the addition of the Kingdom of Léon to Spain. Léon, originally one of the Iberian kingdoms, had become a part of Castille by the start of EU III's timeframe. It was remade as a separate nation for this mod to represent that they were not wholly united. It essentially divided Iberia into six playable nations, while reducing Castille's ability to dominate Spain.
This mod is no longer available, however. Other, larger mods have included León as a playable or releasable country, including Whole World Mod.