Commander, also known as Elder Dragon Highlander, is a casual, originally community-made Magic the Gathering format that is played with 2-4 players, each with a 100 card deck where every card except for basic lands must be unique.
Cardmarket has published a wonderful documentary The Definitive History of Commander that chronicles the history of the format and how it came to be.
I started playing Commander in the fall of 2025 with a Bloomburrow precon Family Matters deck after years of watching Commander gameplay videos from Youtube channels like The Command Zone and Tolarian Community College.