— PRESIDENT BASHAR ASSAD: The 48-year-old Assad has led Syria since 2000, taking over as president after the death of his father, Hafez, who ruled the country for some 30 years. Assad, who trained in London as an ophthalmologist, came to power through a twist of fate: his oldest brother Basil who had been groomed to succeed their father was killed in car crash in 1994, leaving Bashar as the next in line. He quickly showed promise as a young reformer after his father's autocratic government, but those hopes faded before being almost forgotten entirely in the carnage of the civil war.
— AHMAD AL-JARBA: The leader of the main Western-backed opposition group, the Syrian National Coalition. Elected to the post in July, al-Jarba hails from Syria's northeastern province of Hassakeh and is a member of the powerful Shammar tribe that extends into neighboring Iraq. He was a little-known anti-Assad figure before Syria's civil war though he was detained in March 2011—days after the uprising against Assad began. It was his second arrest, following one in 1996 when he was held for two years because of anti-government activities. After his release, al-Jarba left Syria in August 2011 and became active in the opposition. He is widely viewed as being close to Saudi Arabia, and his election as coalition chief was seen as a sign that Riyadh had taken over the mantle as the rebellion's main patron from Qatar.
— JABHAT AL-NUSRA: An Islamist extremist group affiliated with al-Qaida. Jabhat al-Nusra, or the Nusra Front, has emerged as one of the most powerful rebel factions on the battlefield. The U.S. has designated the group a terrorist organization. Jabhat al-Nusra has claimed responsibility for many of the deadliest suicide bombings targeting regime and military facilities. The presence of Islamic extremists among the rebels is one reason the West has not equipped the Syrian opposition with sophisticated weapons, such as anti-aircraft missiles. In recent months, Jabhat al-Nusra has been eclipsed to a degree by the rising power of another al-Qaida-affiliated group—the Islamic State of Iraq and the Levant.
— ISLAMIC STATE OF IRAQ AND THE LEVANT: Al-Qaida's longtime affiliate in Iraq. The Islamic State has moved aggressively in recent months into Syria, and has established a major presence particularly in the north. It has not limited its efforts to fighting the government alone, but has opened fronts against more moderate rebel groups, as well as Syria's Kurdish minority. The group also is known to cooperate with other rebel factions for specific operations. Syrian activists say the Islamic State is largely composed of foreign fighters and has shown a degree of ruthlessness beyond that of Jabhat al-Nusra.
— HEZBOLLAH: The Lebanese Shiite militant group. Hezbollah has sent its gunmen to fight alongside Assad's forces, providing a significant boost to the government's overstretched military. Hezbollah leader Sheik Hassan Nasrallah has suggested he would do everything it takes to save Assad's government, which has been a patron and ally of the militant group for decades. Hezbollah's deep involvement in the conflict underlines the regional sectarian aspect of the conflict, in which an Iranian-backed Shiite axis faces off against Sunnis supported by Gulf Arabs in a proxy war extending into neighboring Lebanon and Iraq.