"King Abdullah's life spanned from before the birth of modern Saudi Arabia through its emergence as a critical force within the global economy and a leader among Arab and Islamic nations," Obama said.
"He took bold steps in advancing the Arab Peace Initiative, an endeavor that will outlive him as an enduring contribution to the search for peace in the region," he said.
The US President said King Abdullah's vision was dedicated to the education of his people and to greater engagement with the world.
"As a leader, he was always candid and had the courage of his convictions. One of those convictions was his steadfast and passionate belief in the importance of the US-Saudi relationship as a force for stability and security in the Middle East and beyond," he said.
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"The closeness and strength of the partnership between our two countries is part of King Abdullah's legacy," Obama added.
Extending his deepest condolences to the people of Saudi Arabia, Republican Senator John McCain hailed King Abdullah as a clear-eyed leader and an important voice for reform in Saudi Arabia.
"He was also a vocal advocate for peace, speaking out against violence in the Middle East and standing as a critical partner in the war on terror. King Abdullah's enduring legacy will continue to shape the Kingdom of Saudi Arabia and the region for years to come," McCain said.
"Our sympathies go to the family of King Abdullah and to the people of Saudi Arabia. King Abdullah was a strong ally of the US and clear-eyed about many of the challenges the Saudi kingdom faces at home and abroad," said Senator Bob Corker, Chairman of the Senate Foreign Relations Committee.