London (CNN) -- Egypt's largest Islamist party, the Muslim Brotherhood, lost its grip on legislative power after the country's highest court declared parliament invalid Thursday.
The Brotherhood dominated parliamentary elections in December, winning about half the seats. But Egypt's interim military rulers -- who have long been at odds with the Brotherhood -- declared full legislative authority in the aftermath of the ruling.
On Monday, however, the party declared that it its candidate Mohamed Morsi had won 52.5% of the votes in the weekend presidential election, putting the party in a position to reclaim power.
What is the Muslim Brotherhood?
The Muslim Brotherhood is a religious and political group founded on the belief that Islam is not simply a religion, but a way of life. It advocates a move away from secularism, and a return to the rules of the Quran as a basis for healthy families, communities, and states.
The movement officially rejects the use of violent means to secure its goals. However, offshoots of the group have been linked to attacks in the past, and critics blame the Brotherhood for sparking troubles elsewhere in the Middle East. Many consider it the forerunner of modern militant Islamism.
When was it created?
The Muslim Brotherhood has been part of the political scene in Egypt for more than 80 years. It was formed there by Hassan al-Banna in 1928.
Teacher Al-Banna and his followers were initially united by a desire to oust the British from control in Egypt, and to rid their country of what they saw as "corrupting" Western influences.
What is its history?
In its early years, the group concentrated on religion, education and social services, but as its membership grew, it moved into the political sphere, organizing protests against the Egyptian government.
In the 1940s, an armed wing of the Brotherhood was blamed for a string of violent acts, including the assassination of Egyptian Prime Minister Mahmud Fahmi al-Nuqrashi in 1948 -- shortly after he had ordered the dissolution of the MB.
Al-Banna himself was assassinated soon afterwards -- his supporters claimed he had been killed on the wishes of the government.
The movement went underground in the 1950s, and decades of oppression by successive Egyptian rulers led many of the Brotherhood's members to flee abroad, while others were jailed.
The MB grew throughout the 1980s as part of a general growth of interest in Islam, and the U.S.-led invasion of Iraq in 2003 saw a spike in membership.
Why is it important in Egypt?
The Brotherhood is the oldest and largest opposition group in Egypt. It has widespread support among Egypt's middle classes, and its members control many of the country's professional organizations.
Up until last year, it was illegal under Egyptian law banning all parties based on religion. But in December, it dominated parliamentary elections, winning about half of the seats up for grabs.
How influential is the Brotherhood elsewhere?
There are branches of the Muslim Brotherhood in countries across the Middle East and North and East Africa, including Sudan, Syria and Saudi Arabia. There is also a branch in the U.S.
Its offshoots outside Egypt are markedly more conservative in their views: The Kuwaiti branch is said to oppose the right of women to vote.
Sayyid Qutb, a member of the Muslim Brotherhood in the 1950s and 1960s, developed the doctrine of jihad, and the radical group Hamas is believed to be an offshoot of the Palestinian Muslim Brotherhood.