UNITED STATES: PRESIDENT DONALD TRUMP
The US President's visit to Riyadh last month may have emboldened Saudi Arabia to move against Qatar, analysts say. Mr Trump tweeted support for the Saudi-led blockade initially but seemingly retracted by expressing Washington's readiness to join efforts to resolve the Gulf crisis.
SAUDI ARABIA: KING SALMAN (ABOVE); DEPUTY CROWN PRINCE MOHAMMED BIN SALMAN (BOTTOM)
Saudi relations with Qatar have long been strained. Reasons include Al Jazeera's criticism of the Saudi government and when the neighbours backed opposing sides in Egypt after the military ousted the country's first democratically elected President Mohammed Mursi of the Muslim Brotherhood. Deputy Crown Prince Mohammed bin Salman, who is also Defence Minister, is increasingly seen as the power behind the throne.
QATAR: EMIR SHEIKH TAMIM BIN HAMAD AL-THANI
Sheikh Tamim had been deeply involved in decision-making even before he became emir in 2013. Qatar's support for the Muslim Brotherhood and its friendship with Shi'ite-majority Iran have irked Sunni-ruled Saudi Arabia, which sees Iran as a rival for influence in the region. Qatar also hosts the largest US airbase in the region, in part to guard against Saudi Arabia.
UNITED ARAB EMIRATES: CROWN PRINCE OF ABU DHABI SHEIKH MOHAMMED BIN ZAYED AL-NAHAYAN
The Crown Prince had met Saudi King Salman in Jeddah two days before the announcement to cut ties with Qatar. Sunni monarchies like the UAE likely rallied behind Saudi leadership and against Qatar as they fear uprisings at home.
TURKEY: PRESIDENT RECEP TAYYIP ERDOGAN
The Turkish leader has tried to play peacemaker even as he denounced the isolation of Qatar as a violation of Islamic values and akin to a "death penalty". Mr Erdogan, whose AK Party has its roots in Islamist politics and who has voiced support for the Muslim Brotherhood, signalled his support for Qatar by signing a law to deploy troops there. He has sent his foreign minister to Qatar, Kuwait and Saudi Arabia to help repair the rift.
EGYPT: PRESIDENT ABDEL FATTAH EL-SISI
The Egyptian leader praised Mr Trump for his role in forming "a united front to combat terrorism" after the US President showed support for cutting ties with Qatar. Egypt, a major power broker in the Arab world, was among the first to support the decision to boycott Qatar, after a visit to Cairo by the Saudi Foreign Minister.
WASHINGTON POST, REUTERS, ASSOCIATED PRESS, NEW YORK TIMES