Former Iranian President Ali Akbar Hashemi Rafsanjani has registered for June's presidential election.
Rafsanjani, who was president from 1989 to 1997, is seen as a threat to Iran's clerical elite around Supreme Leader Ayatollah Ali Khamenei.
President Mahmoud Ahmadinejad, who has served two terms, is not eligible to run again. Ahmadinejad's choice for the next Iranian president is his ally, hardline nationalist Esfandyar Rahim Mashaie.
Other candidates include Ali Akbar Velayati, a top adviser to Ayatollah Khamenei on international affairs, and Iran's chief nuclear negotiator, Saeed Jalili.
More than 400 candidates have registered for elections but Iran's Guardian Council - a body controlled by the supreme leader - decides who can stand.
The results of the last presidential elections, in 2009, were disputed by the reformist opposition, triggering mass street protests.