Determining the single most popular Discord server can be quite subjective and can change over time as new communities emerge and existing ones evolve. However, some of the largest and most well-known Discord servers include gaming communities like "Official Fortnite," "League of Legends," and "Minecraft." Additionally, servers related to popular content creators, streamers, or YouTubers often attract large followings. Ultimately, the "most popular" Discord server may vary depending on factors such as user demographics, interests, and trends.