What Is Commander – What Makes an MTG Card a Commander

For a card to be considered a commander in Magic: the Gathering, it must fulfill one of the two following criteria:

The card must be a legendary creature; or,
The card must state, “This card can be your commander.”
Commanders are always either a creature or planeswalker. This is the first decision a player must make when building a Commander deck: who will lead your army?

The Importance of a Commander’s Color Identity
A commander’s color identity is the combination of colors required to pay for its mana value. For example: Muldrotha, the Gravetide costs six mana to cast: three colorless, one blue, one black, one green. Therefore, Muldrotha, the Gravetide’s color identity is blue/black/green, also known as Sultai in Magic.

During each of your turns, you may play a land and cast a permanent spell of each permanent type from your graveyard. (If a card has multiple permanent types, choose one as you play it.)

Here’s the kicker: Commander decks must conform to the color identity of its commander. In the example of Muldrotha, the Gravetide: the deck can only include cards that are blue, black, green, colorless, or some combination of those colors.

In other words, the color identity of your commander limits what cards you can include in the deck (it is the only limitation, in fact, aside from the ban list).