Sivriss, Nightmare Speaker

If a card refers to a commander creature you own, a Background won't usually be counted or included for that effect. If another spell or ability causes your Background to become a creature, however, it will be included. Any effect that refers to your commander or a commander you own or control without specifying creature will apply to a Background that is your commander, as appropriate.

Once the game begins, your two commanders are tracked separately. If you cast one, you won’t have to pay an additional 2 generic mana the first time you cast the other. A player loses the game after having been dealt 21 combat damage from any one of them, not from both of them combined (although your Background won’t usually be a creature anyway).

If Sivriss somehow becomes an artifact, you may sacrifice it to its own ability.