A memorial march is due to be held in Nigeria for a champion of the environment who confronted one of the world's biggest oil companies - and was then hanged.

It is the 20th anniversary of the execution of Ken Saro-

Wiwa, who campaigned against oil pollution in the oil rich Niger Delta by Royal Dutch Shell.

He was sentenced to death after being found guilty of involvement in four murders - in a case condemned as a sham and after international appeals for clemency.

Al Jazeera's Yvonne Ndege has been to meet his widow in Ogoni - who is proud of his fight against Royal Dutch Shell and for democracy.

Source: Al Jazeera