A poised, articulate and ever-measured counterpart to her father’s brash, freewheeling style, Ivanka will introduce the Republican presidential nominee in Thursday night’s grand finale of the party’s convention. She will be the last of four Trump’s children to speak—and the last to have the chance to humanize her polarizing father for the American people, showing warmth between his rougher edges and heart behind his bluntness.

“There is no one closer to my father than Ivanka,” her brother, Don Jr., said in an emailed statement. While he said his father is close with all of his siblings, Don Jr. said “his bond with Ivanka is truly unique. No one is more poised and articulate than my sister and no one will do a better job of explaining to the American people who my father really is.”

Ivanka Trump spends far less time on the campaign trail than her brothers and her Twitter feed is rarely political, instead focusing on her clothing line and the family business. But she is also her father’s not-so-secret weapon, one who steps into the breach at the most crucial moments.

That began in the campaign’s very first moments, when she assumed a role typically held by political spouses. She introduced the celebrity businessman in June 2015, moments before he took his famous escalator ride to announce his then-quixotic presidential campaign.

“I remember him telling me when I was a little girl, ‘Ivanka, if you’re going to be thinking anyway, you might as well be thinking big,'” she said then. “And that’s how he approaches any task that he undertakes. He thinks big.”

Ivanka Trump spent many months of the primary campaign pregnant with her third child and her father would joke how wonderful it would be if the baby was born in whichever state he was currently campaigning, from Iowa to New Hampshire to South Carolina.

She gave birth to her son, Theodore, on March 27—but appeared in public again just 11 days later to again be at her father’s side at a crucial moment.

Trump had just taken a bruising defeat in Wisconsin and for the first time in months, his campaign seemed vulnerable. The #NeverTrump movement gained steam and the Republican establishment seemed poised to mount one last charge to sink the celebrity businessman’s campaign. But as the primaries shifted to New York, Ivanka made a surprise appearance to kick off her father’s campaign in his native state with a spirited introduction at a massive, raucous rally in Bethpage, Long Island.

Trump won New York in a rout and his Republican primary opponents never again mounted a serious challenge.

“Ivanka is a terrific person, a wonderful mother and someone everyone has great respect for. She is highly intelligent and extremely talented, and I rely on her both for my company and my campaign,” Trump told The Associated Press in a statement. “She has great instincts in business and in life. I am incredibly proud of my daughter Ivanka, all of her accomplishments and especially her beautiful family.”

Trump has long relied on his children in business. Ivanka, Don Jr. and Eric all hold executive positions at the Trump Organization, working in side-by-side-offices a floor below their father’s.

That same family-driven model has extended to politics. Trump’s children now play a central role in his campaign, occupying much of his inner circle and assisting him in decision-making. When his plane was grounded with mechanical delays just as Trump was working to settle on his running mate, he flew them out to join him in Indiana to spend time with the state’s governor, Mike Pence, his ultimate choice.

And while all of his grown children have had a visible presence on the campaign trail, all seem to agree that none is closer than Ivanka, 34, and husband Jared Kushner, who is now involved with nearly all facets of the campaign. That’s in addition her role managing her own eponymous line of clothing, shoes and handbags marketed to working women, and her position as executive vice president of acquisitions and development at the Trump Organization.