Murtadha Ansari
| Murtadha al-Ansari al-Tostari | |
|---|---|
| مرتضی الأنصاري التستري | |
| Title | Grand Ayatollah | 
| Personal life | |
| Born | 1781 | 
| Died | 1864 (aged 82–83) | 
| Resting place | Imam Ali Shrine | 
| Nationality | Arab | 
| Other names | Sahib al-Makasib, Arabic: صاحب المكاسب Sheikh al-Ta'ifa, Arabic: شيخ الطائفة | 
| Relatives | Jabir ibn Abd Allah al-Ansari (ancestor) | 
| Religious life | |
| Religion | Islam | 
| Institute | Najaf Seminary | 
| Jurisprudence | Twelver Shia | 
| Muslim leader | |
| Based in | Najaf, Iraq | 
| Post | Grand Ayatollah | 
| Period in office | 1849–1864 | 
| Predecessor | Muhammad Hasan al-Najafi | 
| Successor | Mirza Shirazi | 
Grand Ayatollah Sheikh Murtadha al-Ansari al-Tostari (1781–1864; Arabic: مرتضی الأنصاري التستري) known as Shaykh al-Ta'ifah (Arabic: شيخ الطائفة, romanized: Shaykh al-Ṭāʾifah) was an Arab Islamic scholar who was “generally acknowledged as the most eminent jurist of the time". He is considered to have laid the foundation of modern Shii jurisprudence, and his style has been imitated more than any other classical scholar of Shia Islam.
Ansari has also been called the "first effective" model or Marja of the Shia or "the first scholar universally recognized as supreme authority in matters of Shii law".