UN High Commissioner for Human Rights Louise Arbour says she is stepping down after four years in the post.
Louise Arbour has a reputation for being tough and uncompromising
Ms Arbour, a Canadian legal expert, told the Human Rights Council she would quit when her term expired in June. She said it was for personal reasons.
Correspondents say she has angered some UN member states by taking a tough stance on their human rights records.
They say that, like her predecessors, Ms Arbour faced criticism from a wide range of countries.
However she denied that was the reason she was quitting.
"It is very much for personal reasons. I'm not prepared to make this commitment for another four years," she told the Council.
She added that ruffling feathers was part of the job.
"It would be surprising or unimaginable to do this work for four years and to depart with unanimous accolades from all players, you would have to wonder about the quality of work," she said.
Ms Arbour came to international prominence in 1996 when she was named chief prosecutor to the UN war crimes tribunal in The Hague.