Fallon talked with Gordon-Levitt about turning 40 and how he has been acting for 30 years. The late night host displayed a photo the actor released on Twitter as Bully No. 2 on Family Ties when he was 7-years-old.
"I remember we all just looked up to him so much, this whole classroom full of young actors. He could have easily not cared, but he did. He took the time to talk to us and encourage us and be really positive with us," Gordon-Levitt said about Fox.
"I actually got to see him again all these years later and man-to-man say like, 'Dude, I was seven on your set and you made a difference to me. Like you inspired me and encouraged me and you showed that like, an actor on a set doesn't have to be like a stuck-up actor, but can be a down-to-earth positive guy with kids who has time for everybody,'" he continued.
Gordon-Levitt said it meant a lot to him and he still remembers the experience.
"He's just the sweetest guy," he added.
Gordon-Levitt has been living in New Zealand and praised the country's handling of the COVID-19 pandemic.
"I feel just so lucky. I almost feel guilty talking about it sometimes because if you don't know, New Zealand's one of like only two countries in the world that's just contained the pandemic. There aren't cases here," Gordon-Levitt said.
"So much of the world is going through such a hard time and people are getting sick and dying and here we are, and I get to go to work every day and not wear a mask," he continued before praising New Zealand Prime Minister Jacinda Ardern.
Gordon-Levitt and Fallon also took on the Face It Challenge where the duo were given random faces to make such as a "bad driver's license photo." The first one to break or start laughing would lose the round.
Fallon and Gordon-Levitt also portrayed the world's happiest dog, dead eyes and a bass player feeling the groove.