The Kingdom of Saudi Arabia was formed in 1932 by the union of Hejaz and Nejd, which had been under the same emir since 1925.

Nejd
The emirate of Nejd, in the centre of Arabia and with capital at Riyadh, was always independent, and was unified by Wahhabi emirs around 1800. Sources sometimes disagree slightly about years, even into the 1900s. This is (I think) Eastern Nejd, which conquered an emirate of Western Nejd in 1892.

  1. Muhammad ibn Saud 1744-1765
  2. Abdulaziz ibn Muhammad 1765-1803
  3. Saud ibn Abdulaziz 1803-1814
  4. Abdullah ibn Saud 1814-1818
    Deposed 1818 and Turkish rule lasted in Riyadh until 1824.
  5. Mishari ibn Saud 1819-1820
  6. Turki ibn Abdullah 1821-1834
    a grandson of Muhammad ibn Saud
  7. Faisal ibn Turki 1834-1837
  8. Khalid ibn Saud 1837-1841
  9. Abdullah ibn Thunaian 1841-1843
    a descendant of Saud ibn Abdulaziz
  10. Faisal ibn Turki restored, 1843-1865
  11. Abdullah ibn Faisal 1865-1871
  12. Saud ibn Faisal 1871
  13. Abdullah ibn Faisal restored, 1871-1873
  14. Saud ibn Faisal restored, 1873-1875
  15. Abdurrahman ibn Faisal 1875-1876
  16. Abdullah ibn Faisal restored again, 1876-1887
  17. Muhammad bin Rashid 1887-1897
    a usurper
  18. Abdulaziz ibn Mitab 1897-1902
    connected with the Rashidi usurpation but I don't know how
  19. Abdulaziz ibn Abdurrahman 1902-1932(-1953)
Abdulaziz, commonly called Ibn Saud, was the son of Abdurrahman ibn Faisal and restorer of the Saudi dynasty: Emir of Nejd 1902, conquered Hasa 1914, Asir 1920, Hejaz 1925, King of Hejaz 1926, Sultan of Nejd 1927, King of Saudi Arabia 1932.

Hejaz
Hejaz is the coastal country containing Mecca. It was taken by Egypt at the beginning of the nineteenth century then by Turkey in 1845. In the Arab Revolt of 1916 it became independent under the Sharif, the ruler of Mecca.

  1. Hussein ibn Ali 1916-1924
  2. Ali ibn Hussein 1924-1925
  3. Abdulaziz ibn Abdurrahman 1925-1932(-1953)
Saudi Arabia
  1. Abdulaziz ibn Abdurrahman "Ibn Saud" 1932-1953
  2. Saud 1953-1964
  3. Faisal 1964-1975
  4. Khalid 1975-1982
  5. Fahd 1982-
All kings after the first have been his sons; the element "ibn Abdulaziz" is omitted because they are familiar under their own name. The word ibn means "son of", and genealogy can usually be tracked by bearing in mind that succession passes to brothers as often as to sons. X ibn Y will be the son of the latest ruler named Y above him in the list. I have tried to note wherever the succession did not follow that principle.