Nelson Mandela has changed a good deal in appearance since he went to prison 25 years ago this week.

I spent three years in the same section of Robben Island prison he occupied while I was serving a seven-year sentence. I was released in March this year. Mandela was imprisoned in 1962, although his life sentence was only handed down in 1964.

The man I saw on the Island had lost the lighter, coffee-coloured complexion of his youth. He is darker now. Prison life has preserved him and others like him from the hazards of life outside prison, but he has not completely escaped the demands of old age.

His 69 years have robbed him of some of the energy with which he conducted his legal practice in the hustle and bustle of the Johannesburg Magistrate's Court during the Fifties. He walks slowly, looking straight ahead, as if in deep thought.

Nevertheless Mandela is still a tall, powerful and fit man. He has a slight stoop and a lick of grey hair on his temples, but he is flat-bellied and has not developed the paunch that characterises many of his contemporaries in prison. He no longer wears his hair with the deep side-parting that can be seen in pre-prison photographs of him.

The last time I had seen him was during his lawyer days when he used to frequent the Blue Lagoon, an elegant black-owned restaurant in pre-Group Areas Act Johannesburg. Since then he has developed two conspicuous wrinkles running on both sides of his mouth.

He is known to fellow prisoners by his clan name, Madhiba. Warders call him Mandela, though most inmates are simply referred to by their prison numbers. I remember one sergeant in particular even calling him Mr Mandela -- unheard of on Robben Island. He has the respect of prison officials.

Mandela is a soft-spoken man of good manners, a gentleman through and through. His impeccable English is tinged with a Xhosa accent. He is proficient in both official languages and in "fly-taal", the township parlance of the 1950s. He has the habit of saying, "Okay, boy", to anyone and everyone.

Despite the tight security in his section of Robben Island, he is well-informed about all his fellow inmates and delves into the family history of whomever he meets. In fact, he knows a good deal on almost every subject and is well-versed about political events in the world. His ideal is a classless society.

He is committed to the realisation of the Freedom Charter, which he describes as a "living document that reflects the will of the people". The charter is, according to his vision, a foundation on which a new South Africa could evolve. The charter, he says, is not the end of the road; it is a means to an end.

Madhiba is well-read. His greatest interest is political economy and any information he can get on the struggles of people in other countries, such as Cuba and Nicaragua. He takes books of this sort out of the prison library and reads newspapers. He is fond of classical music, particularly Handel. He can often be heard singing Handel's "Unto us a child is born", waving his arms around like a conductor. He never participated in the annual year-end prisoners' concert on Robben Island, but he always listened attentively, commenting and criticising.

He usually wears prison-issued fawn trousers and a green shirt. Often he can be seen in a blue toweling gown from the hospital -- especially after exercising or when relaxing, reading and writing in his cell. When we were both on Robben Island, Madbiba would rise early in the morning and skip for exercise. He was a boxer in his youth and can still be seen shadow boxing from time to time.

During the day, I would see him spending a lot of time walking up and down the prison courtyard, deep in conversation with one of his colleagues. His closest comrades are Walter Sisulu, Raymond Mahlaba, Ahmed Kathrada and Wilton Mkwayi, all of whom were involved in the Rivonia trial.

He always seems to be conversing with some prisoner or another. Many prisoners go to him with their problems, whether legal or personal, because cause of his wisdom and his leadership. He is consulted on political issues and current events, and his advice on matters of law is sought very often. He continues to practice his law in prison.

Inmates have all sorts of legal issues to tackle and he is often in consultation with his colleagues, a way of overcoming the difficulties prisoners have in seeing their legal representatives regularly. He often helps prisoners draft the instructions they send to their lawyers outside of prison.

In fact, he is so busy one often has to make an appointment with him if one wants to talk to him. One can meet him anywhere in the prison -- in the courtyard or bathroom -- and a casual chat will lead to a need for a solid discussion. He keeps quiet for a while, thinking how and when he can squeeze you into his packed -- though unwritten -- diary. He does not take matters lightly.

Before a discussion, he consults the relevant available literature and prepares fully. Sometimes you ask him a question in conversation and he does not want to answer there and then; he goes off and thinks about it and sometimes even writes a lengthy paper giving his answer. He is a good writer, though his words are always difficult to read. He writes in tiny, barely legible script, because, he says, of the scarcity of paper in prison.

I sat and ate with him in his cell when it was my turn to exchange thoughts with him. He would offer visitors to his cell what we called "niceties", tinned fond or nuts bought from the prison shop. Meanwhile, Madhiba, a simple cater, would often chew on some dry bread. He never smoked -- though he kept an ashtray under his bed for fellow prisoners.

He is a good listener. Often it seemed to me that my voice had put him to sleep, but when I challenged him he would repeat to me everything I had said. He talks about everything from township life to prison, from his escapades in Africa when he left the country illegally in 1961 to his days in the ANC Youth League.

His Island cell was 2,5m square. As one catered, there was a three door wooden cupboard on the left, containing his clothes, and two shelves above it, packed with books. One would always find legal documents, notebooks and files in piles on top of his cupboard.

His cell was always one of the neatest on the Island, with every paper filed in its place. He is meticulous. A high hospital bed, prescribed for him by doctors, was on the right-handside of the room. Underneath the bed he stored cardboard boxes, filled with books and groceries.

Across the far wall of the cell, stood a table which spanned the width of the room. A wooden sculpture given to him by a prisoner stood on the table. A high back chair stood before the table. A colour photograph of a traditionally-dressed African woman in rural surroundings, cut from Readers Digest' stood on the table.

A black and white picture of his family hung on the wall above his bed. Also on the wall was a homemade calendar with his studying programme. Madhiba had in his cell a chair, also specially prescribed by doctors. The floor was covered by a standard prison felt mat.

Madhiba often speaks about his wife, Winnie, and his children. He calls his wife Zami, from her real name, Nomzamo. For many years, he was concerned that prisoners' children could only see their parents through a glass window. "How can a child grow up without ever touching its father?" he would say. He was always campaigning for a change in this rule, until it was finally granted a few years ago.

I never saw Mabhida angry. He always preached self-restraint and encouraged people in a crisis not to react immediately but to wait till matters had cooled off. However, he is not infallible. He is always ready to apologise or admit he was wrong. He can take criticism. He often says, "if you are a member of the ANC, you must be in a position to defend its virtues and its vices" -- what he called, jokingly, the double-y. He has the habit of sleeping for a while during the day, and writing and reading late into the night.

On Robben Island, he usually attended the film screenings every Saturday, his favourite being the educational documentaries -- that are sent from the provincial library. However, he seldom lasted through the feature film, catching a number of catnaps or leaving quietly to relax in his cell or meet someone.

Mabbida often goes to church, regardless of the denomination of the priest in attendance that day. He is not a religious man, and I am not sure whether his trip to church is simply a token visit or whether he does it for the sake of contact with people from outside the prison. Madhiba was transferred in 1983 from Robben Island to Pollsmoor Prison in Cape Town.