Ivanka Trump was reportedly confronted by a fellow JetBlue passenger while boarding a flight on Thursday.

According to TMZ, Trump was on a plane leaving from New York with her husband and her three children when the incident took place. Matthew Lasner, a college professor, later tweeted that it was his husband, Daniel Goldstein, who confronted and harassed Trump. This all occurred while the plane was boarding at JFK Airport, and both Lasner and his husband were removed from the flight. Lasner did not return a request for comment.

JetBlue has since released the following statement:

The decision to remove a customer from a flight is not taken lightly. If the crew determines that a customer is causing conflict on the aircraft, the customer will be asked to deplane, especially if the crew feels the situation runs the risk of escalation during flight. Our team worked to re-accommodate the party on the next available flight.

Here’s what you need to know about Matthew Lasner and the Ivanka Trump incident.

1. He Is a Professor at Hunter College

Matthew Lasner is a professor at Hunter College, as he made clear in the bio of his Twitter account, which he has since deleted.

Lasner has a PhD in Architecture, Landscape Architecture and Urban Planning from the Harvard School of Design, and he teaches housing and urban planning. Some of his courses have included Introduction to Urban Planning, Introduction to Housing, Housing in the Global City, and Housing and the American City. Before coming to Hunter College, Lasner was an associate history professor at Georgia State University in Atlanta.

In addition to teaching, Lasner has published quite a bit of writing about housing and about urban and architectural history, such as the book High Life: Condo Living in the Suburban Century, which won the 2013 Cummings Prize by the Vernacular Architecture Forum. His website says that this book “examines the emergence and growth of co-owned multifamily housing – the co-op and condominium apartment, as well as the townhouse complex — as an alternative to single-family suburbia in the twentieth century.”

Plus, Lasner has written for journals such as the Journal of the Society of Architectural Historians, the Journal of Urban History, Buildings & Landscapes, Planning Perspectives, and the Journal of Architectural Education.

2. He Once Called Donald Trump ‘the Gordon Gekko of Developers’

Because of his vast architecture knowledge, Lasner has been interviewed by a variety of news outlets over the years, and since Trump is such an influential figure in New York City architecture, Lasner is often asked about him.

In a March 2016 interview with AM New York, Lasner said that Trump represents “an ascension of ego, of surface, and of explicitly catering to new wealth,” going on to call him “the Gordon Gekko of developers.” This is a reference to Michael Douglas’ character from the 1987 movie Wall Street, a character defined by his greed and narcissism. His slogan in the movie is “greed is good.”

In an interview with The Washington Post, Lasner talked about the legacy of both Fred Trump and Donald Trump, saying that if Fred Trump’s New York was a home for the upwardly mobile, Donald Trump’s became a home for those who are already quite wealthy.

“What both of them chose to do and how they made their money is so symbolic of the shifting priorities of the city,” Lasner said of Fred and Donald Trump. “After the traumas of the 1970s…the next generation emerges with a very different set of priorities.”

Lasner elaborated on this point in an interview with The Shortlist.

“Trump was part of a new generation that was very proud of its wealth,” Lasner said. “He understood that there was a clientele that was not ashamed or embarrassed of its wealth, and he catered to that by choosing to build something flashy and loud – just like him.”

3. He Says His Husband Chased Ivanka Down to Harass Her

Lasner’s tweets about the Ivanka Trump incident are a bit contradictory. The first one says that his husband chased Ivanka Trump and Jared Kushner down to harass them. Lasner adds the hashtag #banalityofevil.

But in subsequent tweets, Lasner says that his husband did not harass Trump but instead calmly expressed his displeasure with her. Lasner also snapped a photo of Ivanka Trump and shared it on social media.

Lasner has since deleted his Twitter account.

TMZ reports that Lasner’s husband told Ivanka Trump, “Your father is ruining the country.” He also reportedly asked why Ivanka Trump was flying in coach instead of on a private plane. (Although Trump flew coach, she had Secret Service agents with her and was escorted onto the plane before the other passengers, according to The New York Daily News.)

Marc Scheff, a freelance artist, claims to have witnessed the incident firsthand. On Facebook, Scheff says that the man did not accost Ivanka Trump but that he was also “not what I would describe as calm.” Scheff adds that Ivanka Trump was happy to let the incident go but that JetBlue security made the call to remove the couple.

4. His Husband is Daniel Goldstein, a Brooklyn Attorney

Ivanka Trump Accosted by Passenger on JetBlue Flight https://t.co/1k6rlU93Jv — TMZ (@TMZ) December 22, 2016

Lasner did not name his husband in any of the tweets above. But based on the acknowledgments of a journal article of Lasner’s written earlier this year, his husband can be identified as Daniel Goldstein.

According to a Columbia College newsletter, Goldstein is an employment attorney, and the two were married in September 2012.

Lasner and Goldstein reside in Brooklyn, New York, and have a child, who TMZ reports Goldstein was holding while speaking to Ivanka Trump.

5. He Participated in #NotMyPresident Marches

From his social media profile, it’s clear why Matthew Lasner and his husband might feel compelled to say something to Ivanka Trump, as Lasner believes that Donald Trump is dangerous and he frequently tweets negatively about the president-elect.

For example, a week after the election, Lasner predicted that Trump will open privately-run internment camps. This came around the same time that Trump supporter Carl Higbie cited Japanese internment camps as precedent for a possible Muslim registry, although Lasner’s tweet was posted one day before that comment.

None of the original tweets are now available, but screenshots can be viewed below:

Lasner also retweeted this post begging Ivanka Trump and Jared Kushner to say something about hate crimes committed in Donald Trump’s name.

Dear @IvankaTrump + @JaredKushner, there are swastikas being painted across America by people who support your father. PLEASE SAY SOMETHING. — Michael Skolnik (@MichaelSkolnik) November 11, 2016

And in the days after the election, Lasner participated in #NotMyPresident marches in Chicago, Illinois.