Prince Salman bin Abdulaziz, 76, is the half-brother of King Abdullah and will take the place of the 88-year-old monarch in the event of his death.
Salman, who had been the long-time governor of Riyadh, replaced Crown Prince Nayef, who died Saturday in Switzerland.
Al-Arabiya described Salman as pragmatic, fairly moderate and possessing a keen understanding of Saudi politics. U.S. diplomats said in a 2007 cable posted by WikiLeaks he appeared to favor social reform but preferred a cautious approach that would not unduly shake up the Kingdom's conservative culture.
As defense minister, Salman oversaw a modernization program that recently included sizable purchases of military jets from the United States and Great Britain and was working on a major order for German-built Leopard tanks.