The all-powerful inspector-general of intelligence, Zolile Ngcakani, bared his teeth this week.

In a week when South Africa was rocked by allegations that senior intelligence officers had abused their official positions, Ngcakani came to the fore, acting decisively in an exercise designed to calm fears among citizens of this country.

In his first high-profile case, Ngcakani's work has led to the removal from office of three high-ranking intelligence officials: Billy Masetlha, Gibson Njenje and Bob Mhlanga.

It took Ngcakani just under three weeks to investigate and present reports to Ronnie Kasrils, the intelligence minister, which showed that the National Intelligence Agency had undertaken illegal surveillance of Saki Macozoma, businessman and politician.

Ngcakani, who was appointed in January last year, could not have wished for a more high-profile case to highlight the work of his office. South Africa had been without an inspector-general for two years after the resignation of Faizel Kader.

Kasrils uses superlatives when he speaks of Ngcakani. In introducing him to the media on Friday, the minister emphasised the power that the office of the inspector-general wields.

"His role is to supervise the work of the intelligence community in toto, from the NIA, the South African Secret Service and the National Intelligence Co-ordinating Committee to crime and military intelligence. He ... can investigate any minister. He reports to parliament through the joint standing committee on intelligence," Kasrils said.

On the Macozoma probe, Ngcakani said his terms of reference were to investigate whether such an operation had taken place and whether it was authorised and done within the rules and regulations of the NIA.

"Our findings were that the operation did take place in the manner Macozoma described. It was authorised by the deputy director-general and not disclosed to Kasrils. We found the operation was unlawful and illegal. Its legitimacy was not supported by intelligence information they had," Ngcakani said.

Kasrils was clearly angry that he had not been informed by Masetlha of the decision to put Macozoma under surveillance.

He said the first time he knew about the matter was when Macozoma complained and subsequently submitted a lawyer's letter to back up his claim.

Ngcakani, 68, is no newcomer to intelligence. Between 1996 and 2001 he was head of ministerial services in the intelligence ministry. He provided management and administrative services in support of the ministry's role of control, supervision and superintendence of the intelligence services.

During that period he led several commissions and task teams, such as one to review conditions of service for the intelligence community. Before that, he played a leading role in the establishment of a national communications centre, which provides secure communication services to government as well as an interception office.

Ngcakani is a highly qualified engineer. He has a master's degree in engineering science from the University of Western Ontario in Canada, as well as a master of science degree from the University of Nairobi in Kenya. He is also a water expert, having designed industrial waste water treatment facilities, and has provided advisory services on water quality and water pollution.

Ngcakani's political career started at the University of Fort Hare in the late 1950s. He joined Umkhonto weSizwe, the armed wing of the ANC, and was subsequently based in Zambia and East Africa.

He is married to Pulane and has five children - three girls and two boys.