“I have the great honor to announce that I’ve picked Kamala Harris — a fearless fighter for the little guy, and one of the country’s finest public servants — as my running mate,” Biden tweeted Tuesday afternoon. 

Harris, the daughter of an Indian-born mother and Jamaican-born father, previously served as the first woman, first Black person, and first Asian attorney general of California. While serving in the Senate, she became known for her hard-line, attention-grabbing form of questioning where she often took witnesses to task, especially during investigations into Russia’s meddling in the 2016 presidential elections. 

Harris, 55, who is also the first graduate of a historically black college to potentially hold the position, will work to bring racial, gender, and age diversity to Biden’s campaign. Biden wrote on Twitter that he first came to know Harris when she worked with his late son, Beau, as California’s attorney general, a position she held between 2010 and 2016. “I watched as they took on the big banks, lifted up working people, and protected women and kids from abuse. I was proud then, and I’m proud now to have her as my partner in this campaign,” he wrote.

“This is a historic moment. We’ve only had a woman nominated three times in the country’s history. This is the very first time we’ve seen a woman of color nominated to be on the presidential ticket,” Tina Tchen, CEO of Time’s Up told Fortune. “That’s a moment worth celebrating no matter what your party affiliation.”

As a member of the Senate Judiciary Committee, Harris co-sponsored the first bill to make lynching a federal crime in 2018. She also worked this spring to push police reform legislation in the wake of the killings of George Floyd and Breonna Taylor.

But her no-nonsense views have also stirred controversy. As attorney general, she jailed more than 1,500 people for marijuana-related charges. NORML executive director Erik Altieri told Rolling Stone that her history on drug reform has been “problematic,” and her “record is not one anyone would qualify as progressive, particularly when it comes to marijuana.” She has reversed her stance and now supports progressive marijuana policy. 

Harris also championed a state-wide truancy law that punished and sometimes jailed the parents of habitually truant schoolchildren. She later expressed regret over the policy. 

During the presidential debates, Harris and Biden butted heads over school busing policy in a moment that went viral and brought national attention to Harris’ campaign. Harris said that Biden’s work with segregationist senators like James O. Eastland of Mississippi and Herman E. Talmadge of Georgia was “hurtful.” 

“It was not only that, but you also worked with them to oppose busing,” Harris said. “And you know, there was a little girl in California who was part of the second class to integrate her public schools, and she was bused to school every day. And that little girl was me.”

The pair have since publicly made amends. 

The Trump administration has already launched an attack against Harris with an ad calling her “phony,” among other names. In a statement, RNC chairwoman Ronna McDaniel said that Harris had “extreme” positions “from raising taxes to abolishing private health insurance to comparing law enforcement officials to the KKK.”

“Senator Harris and every woman running for political office are going to face the racist and sexist attacks that have marked women candidates forever,” Tchen said. “These attacks play into the trope that women don’t belong here, and they’re pretending to be leaders. Using this kind of imagery that suggests that women aren’t serious or ready for the job in some fashion is sexist and couldn’t be further from the truth.”

Earlier this month, reports claimed that Biden insiders believed Harris was too “ambitious” for the job, another disproven claim. Numerous studies find that voters are fine with ambitious women, according to Ana Catalano Weeks, a University of Bath comparative politics professor and coauthor of the July paper “Ambitious Women: Gender and Voter Perceptions of Candidate Ambition.”

Harris, meanwhile, has frequently worked with her Republican colleagues in the Senate on an election security bill and a workplace harassment bill. Republican senator Lindsey Graham said of her in May: “I know her. I didn’t like what she did in the Kavanaugh hearings by any stretch of the imagination. But she’s hard-nosed. She’s smart. She’s tough.”

The search for Biden’s vice president has been drawn out and closely watched. In March, during the Democratic primary debates, the former vice president promised that he would choose a woman as his second in command. “There are a number of women who are qualified to be president tomorrow,” he said. “I would pick a woman to be vice president.” In the following months, speculation ran rampant. Names like Harris, Elizabeth Warren, Amy Klobuchar, and Tammy Duckworth were floated as the former vice president’s shortlist grew longer. 

But political and civil unrest reignited after the killing of George Floyd by a white police officer and changed the dichotomy of the decision-making process. Klobuchar, a white woman presiding over Floyd’s state of Minnesota, withdrew herself from consideration, and calls for a woman of color to fill the slot grew stronger. A new list of names, like former chair of the Black Congressional Congress representative Barbara Lee, Atlanta mayor Keisha Lance Bottoms, and former United States ambassador to the United Nations Susan Rice, were added to the mix. 

“My warmest congratulations to Kamala Harris,” Rice, who was thought to be a top pick, tweeted Tuesday. “I am confident Biden-Harris will prove to be a winning ticket. I will do my utmost to help them win and govern.”

Biden felt the pressure mounting to pick a Black woman as his vice president as a group of activists and operatives wrote two open letters to the former vice president last week and on Monday where they said he would need strong Black turnout in swing states like Florida, Wisconsin, and Pennsylvania to win his election. 

“He better pick a Black woman,” Virgie Rollins, chair of the Democratic National Committee Black Caucus, told Politico Tuesday. 

Harris is expected to speak at the Democratic National Convention next week.