Huma Abedin, aide to Democratic U.S. presidential candidate Hillary Clinton. REUTERS/Jim Young Huma Abedin has been by Hillary Clinton's side for decades as one of her longest-serving aides, and now she's at the center of an FBI investigation that involves the Democratic presidential nominee's use of a private email server.

Clinton's critics have long focused on the 41-year-old Abedin because of her close connection to Clinton.

Vanity Fair noted in a profile of Abedin earlier this year that she is often referred to as Clinton's "second daughter." She follows Clinton nearly everywhere and is thought to be one of her closest confidantes.

Abedin started working for Clinton as an intern in 1996 when Clinton was the First Lady. Abedin had initially wanted to go into journalism, but ended up sticking with Clinton and following her from the White House to the Senate to the State Department to the campaign trail. She's now vice-chairwoman of Clinton's presidential campaign.

And the email scandal isn't the first controversy she's found herself at the center of.

Her ties to Saudi Arabia

Abedin's upbringing and family ties have been the sources of many conspiracy theories. She was born in Kalamazoo, Michigan, to a Pakistani mother and Indian father, and she spent much of her childhood in Saudi Arabia.

Her father founded a think tank called the Institute of Muslim Minority Affairs and edited its Journal of Muslim Minority Affairs. Abedin was listed as an assistant editor at the publication from 1996 to 2008. The Clinton campaign has said she did not actually edit articles at the publication, and has noted that her brother and sister are listed as staff members there as well, according to The Washington Post.

Her father died in 1993. Her mother is still an editor at the Muslim journal.

The Post noted that the journal is not radical and that her father was a moderate Muslim.

Her time working for Clinton at State

The Senate Judiciary Committee investigated whether the State Department violated ethics rules by allowing Abedin to remain on its payroll while also doing work outside the government. The department granted Abedin a special waiver to allow her work for the Clinton Foundation, the consulting firm Teneo, and Clinton's private office.

Reuters noted that the waiver Abedin received was initially created decades ago to let the government temporarily bring in experts from the private sector, which wouldn't fit Abedin's description since she had been a government employee for years.

She has also been accused of arranging special access to the State Department for Clinton Foundation donors.

Her marriage to Anthony Weiner

Abedin's involvement in the latest FBI investigation involving Clinton's use of a private email server while she was secretary of state stems from her marriage to former congressman Anthony Weiner.

Weiner resigned from Congress in 2011 in the wake of a sexting scandal. He ran for mayor in 2013, but failed to win the election after yet another sexting scandal came up.

The emails that are at the center of the FBI reopening its investigation were uncovered after the FBI seized devices belonging to Abedin and Weiner, according to reports. Prosecutors issued a subpoena for Weiner's cellphone and other records in late September amid allegations that he had been sexting with a 15-year-old girl.