The head of South Africa's state-owned power company Eskom announced his resignation on Friday in a corruption scandal that has embroiled President Jacob Zuma.
Brian Molefe became the first person to step down after a report released last week raised allegations of corrupt links between Zuma, ministers, top officials and the Guptas, a wealthy business family.
"I have, in the interest of good corporate governance, decided to leave my employ at Eskom," said Molefe in a statement, adding he would depart at the end of the year.
Molefe broke down in tears last week at a press conference where he denied any wrongdoing over accusations in the report, which was drawn up by the Public Protector, the country's top watchdog.
The report included allegations that Zuma ensured the Gupta family won huge preferential contracts with state companies such as Eskom.
Cellphone records obtained by investigators showed that Molefe was at or around the Guptas' home in Johannesburg 19 times between August and November 2015, and made scores of phone calls to Ajay Gupta. Molefe's claim that he may have been at a shebeen (pub) in the opulent area instead led to an internet sensation.
The timing of Molefe's contact with the Guptas raised eyebrows as it coincided with a Gupta-owned firm negotiating the purchase of a mine that supplies Eskom with coal.
"This act is not an admission of wrongdoing on my part," Molefe said in his resignation statement. He said he hoped to prove his innocence and that his name would eventually be cleared.
Economist Peter Montalto from Nomura International said Molefe had "no credibility left" after being named in the watchdog's report. "The rot in Eskom goes much deeper, the whole board needs to be replaced and there are many others there also implicated," Montalto said.
Molefe was appointed Eskom CEO in August 2015, following the suspension of his predecessor Tshediso Matona. The firm has had a series of leadership changes in the past five years, while the country suffered months of regular blackouts last year.
The main opposition Democratic Alliance (DA) welcomed Molefe's resignation, adding it would lay charges against him over alleged corruption. "He has resigned after we began the process of getting him to come clean under oath in parliament," the party said.
Growing numbers of anti-apartheid veterans, ANC activists, trade unions, civil groups and business leaders have called for President Zuma to resign in recent months. On Thursday, he easily survived a no-confidence vote in parliament as the majority ANC lawmakers ignored calls for him to be ousted from office.
South Africa's highest court this year found Zuma guilty of violating the constitution after he refused to repay taxpayers' money used to refurbish his private rural house. He is also fighting a court order that could reinstate almost 800 corruption charges against him over a multi-billion dollar arms deal in the 1990s.