You are probably asking whether Edgar Markov is legal in two-player Commander games. Note the following points.
Edgar Markov is a legendary creature card, so the comprehensive rules do not disallow that card from being in a Commander deck, whether as a commander or not, solely because of its name (C.R. 903.3, 903.2).
Also, the Magic: The Gathering Tournament Rules says nothing on the legality of cards in the Commander variant in particular (review M.T.R. section 6). Of the tournament formats specifically named in section 6 of those rules at the time of this writing, Edgar Markov is legal in Legacy and Vintage.
Third, the Brawl option for the Commander variant usually uses the Standard format (C.R. 903.12b), and at the time of this writing, Edgar Markov is not legal in the Standard format because Commander 2017, which is not a legal Standard set, is the only set that card was printed in (M.T.R. 6.2, 6.3).
Finally, in unsanctioned casual games in general, the players in the game can agree on which cards are banned in a Commander variant game, either generally or as a commander. In this sense, those players may follow one of the many "ban lists" available. For example, at the time of this writing:
See also this thread and this thread, which deals with the similar issue of whether Geist of Saint Traft is allowed in a Commander variant game, and this thread.
EDIT (Apr. 18): One rule was renumbered in the rule update.
EDIT (Sep. 20, 2021): Remove mention of Magic Online.
EDIT (Sep. 30, 2021): Update Duel Commander URL.
Edgar Markov is a legendary creature card, so the comprehensive rules do not disallow that card from being in a Commander deck, whether as a commander or not, solely because of its name (C.R. 903.3, 903.2).
Also, the Magic: The Gathering Tournament Rules says nothing on the legality of cards in the Commander variant in particular (review M.T.R. section 6). Of the tournament formats specifically named in section 6 of those rules at the time of this writing, Edgar Markov is legal in Legacy and Vintage.
Third, the Brawl option for the Commander variant usually uses the Standard format (C.R. 903.12b), and at the time of this writing, Edgar Markov is not legal in the Standard format because Commander 2017, which is not a legal Standard set, is the only set that card was printed in (M.T.R. 6.2, 6.3).
Finally, in unsanctioned casual games in general, the players in the game can agree on which cards are banned in a Commander variant game, either generally or as a commander. In this sense, those players may follow one of the many "ban lists" available. For example, at the time of this writing:
See also this thread and this thread, which deals with the similar issue of whether Geist of Saint Traft is allowed in a Commander variant game, and this thread.
EDIT (Apr. 18): One rule was renumbered in the rule update.
EDIT (Sep. 20, 2021): Remove mention of Magic Online.
EDIT (Sep. 30, 2021): Update Duel Commander URL.