'Abdu'l-Bahá Eldest surviving son of Bahá'u'lláh and His designated successor. Named 'Abbas after his grandfather, 'Abdu'l-Bahá was known as 'Abbas Effendi outside the Bahá'í community. Bahá'u'lláh also gave Him the titles Ghusn-i-A'zam (the Most Great Branch), Sirru'llah (Mystery of God) and Aqá (the Master). He chose the name 'Abdu'l-Bahá (Servant of Baha) for Himself after the passing of Bahá'u'lláh. Source: Momen, Wendi (Ed.): A Basic Bahá'í Dictionary. George Ronald, 1989. ISBN 0-85398-230-9