Who is the servant that lived with Elie and his family?

The only servant of the Wiesel family mentioned in the book is Martha. After the family is transferred to the "little ghetto," Martha pleads with Elie's father to escape with his family to her village:

Our old servant, Martha, came to see us. Weeping bitterly, she begged us to come to her village, where she could give us some refuge. My father did not want to hear of it.

For the last time, Mr. Wiesel refuses to leave Sighet in an attempt to escape Nazi persecution. He tells Elie and the older sisters they could go with Martha if they wanted but that he and his wife and the youngest daughter would remain. Elie's father obviously believed the family would be safe despite the signs that the Nazis were bent on deporting as many Jews as possible. He was wrong.
There are numerous examples of good people like Martha attempting to help the Jews during World War II. Schindler's List, The Diary of Anne Frank, and The Zookeeper's Wife are just a few of the stories where individuals and families risked everything to hide Jews and protect them from the Nazis. Unfortunately, Martha was not able to persuade Mr. Wiesel.