Historical Rules · 8 July 2022
Rule 903.3d
Official source text from the 8 July 2022 Rules release
If an effect refers to controlling a commander, it refers to a permanent on the battlefield that is a commander. If an effect refers to casting a commander, it refers to a spell that is a commander. If an effect refers to a commander in a specific zone, it refers to a card in that zone that is a commander.