Swamp

Black has paid for its color since the beginning, and this is the resource the payment runs on. Every life-loss drain, every reanimation spell, every discard package and removal suite that defines the color traces back to a tapped source producing this single mana symbol. The card itself does nothing but that, which is precisely its design role: it is the floor that the rest of black's power is priced against. When a designer prints a hand-disruption spell at one mana or a reanimation effect at five, the cost is denominated in how many of these a deck can realistically run, and how reliably they enter untapped. That tension (color demands against fixing constraints) is the oldest knob in deckbuilding, and it has not moved since Alpha. Present in essentially every set with a basic-land slot, it is not so much a card as a constant: the fixed point that lets the rest of the game's economy float. Players rarely think about it until they are flooding on it or starved for it, and both of those moments are the card doing exactly what it was built to do: be the thing whose count you got right or wrong three turns ago.