Abu Zakariyya Yahya ibn Umar ibn Talagagin ibn Turgut ibn Wartasin, commonly suffixed al-Lamtuni al-Sanhaji, (d. near Azuggi, 1056) is a chieftain of the Lamtuna of the Branès, part of the Sanhaja confederation of nomadic Berber tribes of the western Sahara Desert.

Yahya ibn Umar is the first emir of the Almoravids in the mid-11th century, a movement he constructsin collaboration with the religious leader Abdallah ibn Yasin.

Yahya leads the Almoravid armies in their first campaigns, including captures of Sijilmassa and Awdaghost in 1054/55, but is himself killed in battle against a dissident Berber faction in the Adrar.

Yahya is succeeded as Almoravid emir by his brother, Abu Bakr ibn Umar.