The Islamic Revolution's Guards (IRG) (Sepah-e Pasdaran-e Enghelab-e Islami), literally: (Army of the Guardians of the Islamic Revolution), or simply is the largest branch of the Islamic Republic of Iran's military.
The present Chief Commander of the Guards is Mohammed Ali Jafari, who was preceded by Yahya Rahim Safavi. Like many young Iranians during the 1980-88 Iran-Iraq war, Iran's current president Mahmoud Ahmadinejad was a member of the Guards. In English language media, the force is usually referred to as the Islamic Revolutionary Guards Corps (IRGC).
The IRG is separate from, and parallel to, the other arm of the Iran's military, which is called Artesh (another Persian word for army). IRG is equipped with its own ground forces, navy, air force, intelligence , and Special Forces. It also controls Basij force, which has a potential strength of eleven million, although Basij is a volunteer-based force, and consists of 90,000 regular soldiers and 300,000 reservists. The IRG is officially recognized as a component of the Iranian military under Article 150 of the Iranian Constitution. 
The force's main role is in national security, responsible for internal and border security, as well as law enforcement.
It is also responsible for Iran's missile forces. The operations of the IRG are geared towards asymmetric warfare and less traditional duties. These include the control of smuggling, control of the Strait of Hormoz, and resistance operations.
Thus, the role of the IRG will complement the more traditional role of the regular Iranian military with the two forces operating separately and focusing on different operational roles.
The IRG were formed in May 1979 as a force loyal to Ayatollah Ruhollah Khomeini, but later became a full military force alongside the army in the Iran-Iraq War. It was infamous for its human wave attacks such as during Operation Ramadan, an assault on the city of Basra
Lebanon Civil War
During the Lebanese civil war, the IRG allegedly sent troops to train fighters in response to the 1982 Israeli invasion of Lebanon . In Lebanon, political parties had staunch opinions regarding the AGIR's presence. Some, mainly the Christian militias such as the Lebanese Forces, Phalanges, and most of the right-wing Christian groups declared war on the AGIR, claiming they violated Lebanese sovereignty. Others were neutral
Groups such as the PSP and Mourabiton did not approve of their presence, but to serve political alliances they decided to remain silent on the matter. This presence has also later been linked to the disappearance of four Iranian diplomats in Lebanon, with the Lebanese Forces being the main culprits
2006 plane crash
In January 2006, an IRG Falcon carrying fifteen passengers crashed near Oroumieh, killing all 15, including 12 senior IRG commanders. Among the dead was General Ahmad Kazemi, the IRG ground forces commander. 
Involvement with Hezbollah
The AGIR's logo was inspiration for the logo of Hezbollah. The IRG provided military training to Hezbollah fighters in the Bekaa valley during the early eighties. Other Lebanese parties[attribution needed] have expressed concern about this relationship but remained neutral as they saw the AGIR's presence in Lebanon as resistance against Israeli presence. This came despite the ongoing fight between the Shiaa Amal militias and the PLO and its Sunni allies
Involvement in the Iraq War
The U.S. DoD (Department of Defense) has repeatedly asserted IRG involvement in the Iraq War, though the US has stopped short of saying the central government of Iran is responsible for the actions.. The Department has reported that it has intelligence reports of heavy Islamic Revolutionary Guard involvement in Iraq in which the force is supplying Iraqi insurgents.  It is further claimed that US soldiers have been killed by Iranian-made or designed explosive devices.
This claim is disputed by Iran, saying that the bulk of American military deaths in Iraq are due to a Sunni insurgency and not a Shiite one. Two different studies have maintained that approximately half of all foreign insurgents entering Iraq come from Saudi Arabia. Iran further disputes that former Iraqi army personnel, whom, prior to the 2003 invasion, the US and UK claimed were capable of deploying advanced missile systems capable of launching WMDs within 45 minutes, would be incapable of designing and producing improvised explosive devices
The U.S. charges come as Iran and Turkey have complained that U.S.-supplied guns are flowing from Iraq to anti-government militants on their soil. The Government Accountability Office (GAO), the investigative arm of the US Congress, said in a report that the Pentagon cannot account for 190,000 AK-47 rifles and pistols given to Iraqi security forces. .
Security analysts with the Centre for Defence Information, along with one senior Pentagon official, suggested that some of the weapons have probably made their way in to the hands of Iraqi insurgents.  Italian arms investigators also recently stopped Iraqi government officials from illegally shipping more than 100,000 Russian-made automatic weapons into Iraq. In January 2007 the US army detained five Iranians in northern Iraq, claiming they were Quds operatives of the AGIR, providing military assistance to Shiite militias. The Iranian and Iraqi governments maintain that they were diplomats working for the Iranian consulate in Iraqi Kurdistan
Designation by the United States as a Terrorist Organization
In August 2007, the Washington Post reported the U.S. government was considering labeling the Revolutionary Guard a "terrorist organization." This possible decision to designate the Guard as a terrorist group, according to Bush administration officials , was based on, "...the group's growing involvement in Iraq and Afghanistan as well as its support for extremists throughout the Middle East." The designation of the Revolutionary Guard would be made under Executive Order 13224, which allows the United States to block the assets of those designated as terrorists and to disrupt operations by foreign businesses that "provide support, services or assistance to, or otherwise associate with, terrorists." 
President Karzai of Afghanistan has argued that Iran is "a helper and a solution" for Afghanistan while Prime Minister Maliki of Iraq has argued that Iran has a "positive and constructive" role in helping the Iraqi government improve security in his wartorn nation. When Voice of America, a U.S.-funded outlet, asked if Iran is supplying weapons to the Taliban, current president of the Islamic Republic of Iran Mahmoud Ahmadinejad laughed and said the US doesn't want Iran to be friends with Afghanistan. "What is the reason they are saying such things?" asked Ahmadinejad.  On October 25, 2007, the United States designated the Islamic Revolutionary Guard Corps and the Ministry of Defense and Armed Forces Logistics (MODAFL) as terrorist organizations. 
References and notes
9. [www.iranfocus.com/modules/news/article.php?storyid=5206 Iran’s top military commanders die in plane crash]
15. (Baer R, See No Evil, 2002, Three Rivers Press, page 250)
32. Fact Sheet:
Designation of Iranian Entities and Individuals for Proliferation Activities and Support for Terrorism