Prominent Iranian scientist Mohsen Fakhrizadeh, killed in an attack outside Tehran on Friday, was widely seen outside the country as a leading figure in the Islamic Republic's nuclear programme. Iran denies his involvement.
WHAT IS KNOWN ABOUT HIM?
Western officials and experts believe Fakhrizadeh played a pivotal role in suspected Iranian work in the past to develop the means to assemble a nuclear warhead behind the facade of a declared civilian uranium enrichment programme.
Iran denies ever having sought to develop a nuclear weapon.
A landmark report by the U.N. nuclear watchdog in 2011 identified Fakhrizadeh as a central figure in suspected Iranian work to develop technology and skills needed for atomic bombs and suggested he may still have a role in such activity.
Believed to be a senior officer in the elite Revolutionary Guards, Fakhrizadeh was the only Iranian the report identified.
WHAT DOES IRAN SAY?
The U.N. International Atomic Energy Agency (IAEA) has long wanted to meet Fakhrizadeh as part of a protracted investigation into whether Iran carried out illicit nuclear weapons research.
Showing no sign it would heed the request, Iran acknowledged Fakhrizadeh's existence several years ago but said he was an army officer not involved in the nuclear programme, according to a diplomatic source with knowledge of the matter.
He was also named in a 2007 U.N. resolution on Iran as a person involved in nuclear or ballistic missile activities.
WHAT IS KNOWN ABOUT HIS BACKGROUND?
An exiled Iranian opposition group, the National Council of Resistance of Iran (NCRI), in May 2011 issued a report with what it said was a photograph of Fakhrizadeh, with dark hair and beard stubble. It was not possible to independently verify the picture.
The NCRI said in the report that Fakhrizadeh was born in 1958 in the holy Shi'ite Muslim city of Qom, was a deputy defence minister and a Revolutionary Guards brigadier-general, and holds a nuclear engineering doctorate and taught at Iran's University of Imam Hussein.