There were many people imprisoned on Robben Island in addition to Nelson Mandela.
It is strange, therefore, that only Nelson Mandela, his cell, his prisoner number, the length of time he served on the Island, etc. are known to the outside world, and possibly only his name is well-known to South Africans.
While members of the African Nationalist Congress, and the Rivonia Trialists, were prisoners on Robben Island, members of the Pan African Congress were also imprisoned there.
Robert Sobukwe, the leader of the Pan African Congress was imprisoned on Robben Island.
My understanding is that the longest serving prisoner on Robben Island was not Nelson Mandela, but the Pan Africanist Congress member JAFTA KGALABI MASEMOLA.
Jafta Masemola died a few months after his release from Robben Island.