Saddu was born in 1558 AD, during the reign of Shah Tahmasp Safavi of Iran. Majority of the writers of repute, namely, Muhammad Hayat Khan, Munshi Abdul Karim, Ganda Singh, Atta Muhammad and Sir Olaf Caroe are of the view that Saddu was the son of Umar Khan Popalzai. At the age of ninety, his father, Umar – eight years before his death – appointed Saddo his successor and performed the ‘belt and sword-girding’ ceremony with his own hands. Saddo was only twenty five years old then. But this talented young man was so promising and popular that his elevation to the chieftainship of the tribe was welcomed and acclaimed by all, including his sixty years old brother Malik Saleh . When Kandahar became a bone of contention between the Mughals and the Safavids , Malik Saddu allied himself with Shah Abbas instead of the Mughal Emperor Jahangir. Malik Saddu, helped Shah Abbas Safavi in conquering Qandahar in 1622 (1032 A.H.). Shah Abbas, therefore, realising Malik Saddu’s importance in the territory of Qandahar, acknowledged his chiefdom and bestowed upon him the government of ‘Safa’ along- with the title of Mir-i-Afghan. He also exempted Alus Abdali and Malik Saddu from paying annual tribute to the Safavid Emperor. Malik Saddu was a great warrior, a politician and a pious man. 
The following are the terms in which Sir John Malcolm, in his work on Persia, speaks of the Afghan embassy sent to Shah Abbas; the information is taken from the Persian manuscript of Mirza Syed Mohamed of Isfahan:—
“In the time of the Safavid kings of Persia the Afghans were often oppressed; and on one occasion they were so discontented with their Persian governor, that they sent a secret deputation to Ispahan to solicit his removal and the appointment of one of their own tribe. Their request was granted; and two of the tribe of Abdali were raised to the office of Reish Safeed, or Kutkhodah of the tribes, and their authority was confirmed by a royal patent. The name of one of these two persons was Saddo, of the family of Bami, from whom Ahmed Shah, the founder of the present royal family of Cabul, is lineally descended. The name of the other was Ahmed, of the family of Barakzai, from whom the present Afghan chiefs, Serafray Khan and Futteh Khan, are descended. The Afghans were delighted with this arrangement, and granted their entire and respectful obedience to the chief appointed by the Persian Government Time has confirmed this respect; and the superiority of the chiefs so selected has become an inheritance to their family. The race of Saddo obtained sovereignty, while that of Ahmed has only gained high station and command.” 
Saddo had five sons, of whom the second, Khwaja Khizr Khan, became the headman of the Khizr Khel clan. Khwaja Khizr was a godly man and is still revered by the Afghans as a favourite saint. The devotion and awe, inspired by this holy personage, lent a sense of sanctity to the whole clan of Saddozais, and its members enjoyed peculiar privileges. Their persons were sacred , no punishment could be inflicted on them , except by one of their own family ; nor could even the head of Abdalis himself pass sentence of death upon a Saddozaey.
Towards the end of his life Saddo wished to appoint Khwaja Khizr Khan the head of the tribe , but his choice was rejected by the chiefs of various clans in favour of Maghdud Khan, Khizr’s elder brother on the ground of his primogenitory right. On the death of Saddo, however, the tribesmen, unanimously elected Khizr Khan to the high office considering him better for its duties and responsibilities.
1- Pakistan Journal of History and Culture – Volumes 1-2 – Page 10
2- Joseph Pierre Ferrier, History of the Afghans, p-22
3- Dr.Ganda Singh, “Ahmad Shah Durrani”, p-2