Mírzá Músá (‎; d. 1887) was the only full brother of Baháʼu'lláh, meaning that they shared the same mother and father. He was later named by Shoghi Effendi as one of the nineteen Apostles of Baháʼu'lláh. The life of Mírzá Músá was so bound up with that of Baháʼu'lláh himself, that his life and background mirror the life and travels of Baháʼu'lláh. He was an integral part of correspondence between Baháʼu'lláh and the Baháʼís. He experienced the same imprisonment, exile, assaults, and degrading circumstances that were given to the small band of family members associated with Baháʼu'lláh and ʻAbdu'l-Bahá. Mírzá Músá remained a loyal and faithful follower until he died. Baháʼu'lláh used Mírzá Músá as an example to show his respect for the law. When an official expressed hesitation to inflict punishment on one of the followers of Baháʼu'lláh who had committed a crime, he replied: He also went by the title of Kalím, Áqáy-i-Kalím (Chief Kalím), or Jináb-i-Kalím (Excellent Kalím).

Family

Mírzá Músá had at least three children: Mirza Majdi'd-Din, Ali Rida, and a daughter. Mirza Majdi'd-Din for a time transcribed the Tablets of Baháʼu'lláh. He was the one who read the Kitáb-i-'Ahd in front of the family upon the passing of Baháʼu'lláh. Later, he supported Mírzá Muhammad ʻAlí, and after his death Shoghi Effendi called him "the most redoubtable adversary of ʻAbdu'l-Bahá".