If the person is still living then interview him/her with questions you think will show the uniquness of the person. Ask questions like - what one thing do you hope people will remember about you? What gives your life meaning? What are you joys and fears?
If the person is no longer living then interview people - friends and realtives who were most close to him/her.
The answers to your inteview qustions should give you a good start on your report.