Angolan ruling MPLA party veteran and historian Ambrósio Lukoki wants former President José Eduardo dos Santos prosecuted.
Mr Lukoki, currently the Angolan ambassador to Tanzania, also wants the former ruler to resign from the Popular Movement for the Liberation of Angola leadership immediately.
Mr dos Santos had in March 2016, indicated he would quit politics in 2018.
Mr Lukoki said at a press conference in Luanda on Tuesday that Mr dos Santos was hiding behind the MPLA leadership to avoid prosecution for the numerous crimes associated with his 38-year rule.
"It is convenient that José Eduardo dos Santos immediately resigns from the MPLA post so that President João Lourenço can operate unhindered," said Mr Lukoki.
Mr Lukoki, 75, was a close ally of the MPLA founder and first president Agostinho Neto, and once served as a member of the MPLA political bureau and the first minister for Education.
Last year, ahead of the MPLA seventh congress, Mr Lukoki asked that his name to be removed from the Committee Central (CC) list. CC is the party's organ and decides on critical political issues.
He, at a brief press conference, said it that it did not make sense for him to remain in the party's decision-making organ as all decisions were imposed.
According to him, the decisions were imposed courtesy of President dos Santos iron-fist rule.
Mr Lukoki also accused President's dos Santos of tarnishing the party's image due to his unpopularity.