Sheikh Nimr al-Nimr, one of 47 people executed in Saudi Arabia Saturday, was a central figure in Shi'ite protests that erupted in 2011 as part of the Arab Spring.
Al-Nimr had been regarded as the most vocal Shi'ite leader in the eastern Saudi province of Qatif. He publicly criticized the ruling al-Saud family, and called for pro-democracy demonstrations and elections.
He was arrested in 2012. At his trial, al-Nimr did not deny the political charges against him, but said he never carried weapons or called for violence.
Saudi Arabia’s Supreme Court rejected an appeal in October against the death sentence passed earlier on al-Nimr.
Carrying out al-Nimr's execution could have serious repercussions in the Sunni kingdom, and may further inflame sectarian tensions in the region.
Al-Nimr's family was shocked by news of the execution, the cleric's brother said, but they hoped reaction to the news would be peaceful.
"Sheikh Nimr enjoyed high esteem in his community and within Muslim society in general and no doubt there will be reaction," Mohammed al-Nimr told Reuters by telephone. "We hope that any reactions would be confined to a peaceful framework. No one should have any reaction outside this peaceful framework. Enough bloodshed."
Iran’s Shi'ite leadership said the execution of al-Nimr "would cost Saudi Arabia dearly."
In a statement aired on its TV network, Asaib Ahl al-Haq, an Iranian-backed Shi'ite militia in Iraq, called on Baghdad to reconsider the re-opening Friday of the Saudi embassy. Saudi Arabia had closed its embassy in Baghdad in 1990, after the late Iraqi dictator Saddam Hussein invaded Kuwait.