Dr. Essam Mohamed Hussein el-Erian, a prominent figure in Egypt's Muslim Brotherhood, died on Thursday due to sudden heart attack or of natural causes, according to Egyptian media sources.

"Prison authorities informed me of the death of Essam Al-Aryan, telling us the death was natural. I do not know if he died in prison or in hospital. I have informed his family of his death and started procedures after his death," said Abdel-Mon'em Abdel-Maqsoud, a lawyer for Muslim Brotherhood leaders.

Egyptian officials had no immediate comment on Al-Aryan's death.

Who was Dr. Essam Mohamed Hussein el-Erian?

El-Erian was born on April 28, 1954. He graduated from the School of Medicine in the Cairo University with honors in 1977, and also received a Bachelor of Law from the same university.

During his time at university, Erian was the secretary of the cultural committee of the federation of students of medicine at the College of Medicine at Qasr Aini in 1972, and then became the president of the general union for students of Egyptian universities.

He earned a master's degree in Pathology in 1986 from Cairo University. He also earned a bachelor's in Islamic Studies and a bachelor's in History from al-Azhar University respectively in 1999 and 2000. El-Erian was enrolled for a medical doctorate at Cairo University and for a degree in common law at the same university, a program he did not complete due to his imprisonment.

He was elected as a member of the board of directors of the Egyptian Medical Syndicate in 1986, with being the assistant of the general secretary of the Egyptian Medical Syndicate. Also El-Erian was a founder member of the Egyptian Organization for Human Rights.

El-Erian was a prominent student leader in the 1970s and coordinated with other students, including Abdel Moneim Aboul Fotouh and Ibrahim El Zafarany to facilitate the entry of many small Islamic organizations into the Muslim Brotherhood.

For many years, he was a member of the Muslim Brotherhood and served on its Guidance Bureau before being the vice chairman of the freedom and justice party founded by the Muslim Brotherhood.

As a leader within the Muslim Brotherhood, El-Erian claims that he worked to ensure that the ideas of the Muslim Brotherhood and Hassan al-Banna conformed with democratic principles, also he's known for his Sufi's tendency.

In 2012 during an interview on Egypt's Dream TV, Erian called on former Egyptian Jews who had immigrated to Israel and their descendants to return to Egypt, and called for all Israeli Jews to return to their countries of origin, be it "Poland, Egypt, or anywhere", and also called for the return of Palestinian refugees.

 Erian stated that although his party was against Zionism, it was not against the Jews, stating that "they have a complicated history, but the Jewish motherland is not Israel".

El-Erian was arrested in 1981, during the famous September arrests that specifically targeted members of Islamist groups in large numbers. He was then tried in a military court for the members of the Muslim Brotherhood. He was imprisoned from 1995–2000, for a span of five years.

After the 2013 Egyptian coup, prosecutors ordered his arrest on 10 July 2013. On 14 July 2013, Egypt's new prosecutor general Hisham Barakat ordered his assets to be frozen. El-Erian was arrested by Sisi government on 30 October 2013. (ILKHA)