In Commander, can your commander be one half of a meld pair?

A card that is part of a meld pair can legally be designated as your commander in the Commander format, provided it meets the usual requirements — it must be a legendary creature card (CR 903.3). For example, Mishra, Claimed by Gix is a legendary creature and is a legal commander choice on its own.

The complication arises with the melded permanent. When two meld cards combine into their melded form (e.g., Mishra, Lost to Phyrexia), the result is a single permanent represented by two physical cards. This melded permanent is NOT your commander — only the original half you designated as commander retains that status (CR 903.3, 701.36). The melded card has its own card name and characteristics separate from either half.

If the melded permanent would leave the battlefield, commander replacement effects only apply to the half that was your designated commander. According to CR 701.36d and Commander rules, the commander half can be moved to the command zone, but the other half goes to whatever zone is appropriate (usually the graveyard) as a separate card.

Concrete example: You designate Mishra, Claimed by Gix as your commander. You manage to meld him with Phyrexian Dragon Engine to form Mishra, Lost to Phyrexia. When Mishra, Lost to Phyrexia dies, you may send Mishra, Claimed by Gix to the command zone, but Phyrexian Dragon Engine goes to the graveyard normally.

Because the meld partner must also reach the battlefield and survive, executing the meld in a Commander game is difficult but not rules-illegal. The key restriction is that the melded permanent itself never becomes your commander.