WASHINGTON • She has worked side by side with Mrs Hillary Clinton for 20 years and is one of the candidate's most trusted advisers.
Ms Huma Abedin, 40, is the vice- chairman of the Clinton campaign.
Mrs Clinton has often said that if she had a second daughter, it would be Ms Abedin, calling her smart, discreet and effective.
Ms Abedin was widely expected to take on a senior role in the White House if Mrs Clinton wins, but that has been thrown into doubt following the new e-mail inquiry.
The latest batch of e-mails was found in the laptop of her estranged husband, former congressman Anthony Weiner, who has been embroiled in sexting scandals.
Born in Michigan to educator parents from India and Pakistan, Ms Abedin spent her childhood in Saudi Arabia before returning to the United States to attend graduate school.
She arrived as an intern at the White House in 1996 and was assigned to the Office of the First Lady. She then followed Mrs Clinton when the latter became New York senator in 2001 and became her chief of staff. She was Mrs Clinton's personal assistant when the candidate launched her failed 2008 presidential bid.
When Mrs Clinton became secretary of state in 2009, Ms Abedin became her deputy chief of staff.
Under a special arrangement, she was allowed to work as a consultant for Teneo, a consulting business related to the Clinton Foundation, while also working for the foundation. Some of Ms Abedin's e-mails during that time have led to accusations that foundation donors had received special access to the State Department.
Mrs Clinton played a part in introducing Ms Abedin and Mr Weiner. In August 2001, he asked Ms Abedin if she would go out for a drink. Ms Abedin shook her head but Mrs Clinton told her to go.
In 2010, Ms Abedin, who is Muslim, wed Mr Weiner, who is Jewish, in a ceremony officiated by former US president Bill Clinton.
The couple have a son, Jason, born in December 2011.
Mr Weiner resigned his congressman post in May 2011, after acknowledging that he sent pictures of himself in underwear to women on Twitter. In May 2013, he plotted a political comeback, announcing his candidacy for New York mayor.
Two months later, new charges surfaced that he continued to send lewd messages on social media.
Ms Abedin, in a documentary released this year on his failed campaign, said she loves her husband and had forgiven him. But more sexting allegations followed. In August, she separated from him.
In the same month, a report in the New York Post said that she once had an active role at a Muslim journal - founded by her late father and now headed by her mother - that has published articles which refute major tenets of Mrs Clinton's campaign. The Clinton campaign denied the report.
Describing her ties with Mrs Clinton, Ms Abedin recently told Vogue magazine: "The nature of our relationship has changed. Over the years...we've celebrated together, we've mourned together."
AGENCE FRANCE-PRESSE, NYTIMES