Rabbi Andrea Weiss, an associate professor of Bible at the New York campus of Hebrew Union College-Jewish Institute of Religion and its incoming provost, remembered the joy that Rabbi Aaron Panken brought to his work. Weiss recalled how Panken would pop into his colleagues’ offices asking if they were having fun.

“He had this very serious position as president of a very large institution, and he approached it with such joy and with kind of a boyish enthusiasm. He really loved his work,” she said.

Friends and colleagues of Panken, the president of HUC who died Saturday in a plane crash, remembered him as a strong leader who was passionate about Israel and, above all, loved what he did as the leader of the Reform movement’s flagship seminary and its campuses in New York, Jerusalem, Cincinnati and Los Angeles. He was 53.

“They say that no person is irreplaceable, but Aaron Panken … is the exception to the rule,” said his friend of many years, Rabbi Beth Singer of Congregation Emanu-El in San Francisco. “He combined intellect, talent, humility and a heart of gold. We all know ridiculously smart people. We all know ridiculously kind people. Aaron was both, all the time. His loss is incalculable.”

Jean Bloch Rosensaft, HUC’s assistant vice president for communications and public affairs, said Panken embodied “the best of the Reform movement.”

Speaking to JTA, Rosensaft said, “The college was his whole life. He was a real product of the Reform movement, and he was proud of it.”

Panken, who had led HUC since 2014, was killed while piloting a small aircraft near Wawayanda, New York, near the New Jersey border. The lone passenger, flight instructor Frank Reiss, 65, was injured in the crash, the cause of which was unclear pending investigation by the the Federal Aviation Administration and the National Transportation Safety Board. Panken was a licensed pilot.

His sister-in-law, Daryl Messinger of Palo Alto, the national chairperson of the Union for Reform Judaism, was devastated. “I lost a brother-in-law, but all of us have lost a great leader who had an enormous impact on Reform Judaism and Jewish life in North America and around the globe,” she said. “Despite being an extraordinarily brilliant rabbi, visionary and scholar, he was exceptionally approachable, curious and loved learning from all.”

Before serving as HUC president, the native New Yorker held senior positions at the school, including vice president for strategic initiatives, dean of the New York campus and dean of students.

Provost Michael Marmur said May 7 that the school had yet to make succession plans but would have an announcement regarding the issue in the coming days. HUC is holding memorial services on all of its campuses this week, and a livestream of his funeral at 1 p.m. EDT Tuesday, May 8 at Westchester Reform Temple in Scarsdale, New York, is slated to be shown at wrtemple.org.

Rosensaft said Panken was passionate about Israel, working to improve ties between American Jews and the Jewish state, and strengthen Reform Judaism there.

“This was the mission of his life, and he really lived it with every fiber of his being,” she said.

Panken started several Israel-related programs, including one that brings Israeli rabbinical students and graduates to visit the U.S. to learn more about Jewish life here. Another program, in partnership with the Foreign Affairs Ministry of Israel, strengthens ties between young Reform Jewish leaders and Israeli political and key cultural figures. He also created a program that brings Jewish, Christian and Muslim school teachers in Israel to the HUC Jerusalem campus to learn about tolerance.

“He was creating change and working toward positive change in Israeli society in order to strengthen Israel,” Rosensaft said.

Singer met Panken decades ago in Israel, and both worked at Westchester Reform Temple in New York in 1989. He was the rabbinical student intern and she was a newly ordained rabbi. The two became lifelong friends, she recounted.

“At every rabbinical conference, Aaron, my husband Jonathan and I always took time to go out together for a meal or a drink, let our hair down and share our confidences with one another,” she said.

“Aaron was a superb scholar-in-residence at our synagogue in Seattle,” Singer added. “Out to dinner one night, [Jonathan and I] revealed that we were being offered positions as co-senior rabbis at Congregation Emanu-El in San Francisco and he was mulling over an offer to become President at HUC-JIR. We three laughed and marveled that we were each headed on such special paths.”

Marmur, who worked with Panken for some 20 years, said Panken had a talent for making others excited about what was happening at HUC.

“He was one of those rare people who could really get people on board and get them excited about a vision for this place. He was tireless,” Marmur said.

Weiss said Panken was dedicated to supporting the HUC faculty. She recalled speaking to him about an idea for a project to have 100 religious leaders write letters about American core values to President Donald Trump to be delivered on the first 100 days of the new administration.

The following day, he returned and wholeheartedly threw his support behind it.

“He was the kind of person who really helped nurture people to be their best and helped people grow professionally,” Weiss said.

Marmur also remembered Panken as “a very devoted friend and incredibly devoted family man.”

Panken lived with his family in Scarsdale, New York, and was a member of the Westchester Reform Temple. He is survived by his wife, Lisa Messinger; his children, Eli and Samantha; his parents, Beverly and Peter; and his sister, Rabbi Melinda Panken of Congregation Shaare Emeth in Manalapan, New Jersey.