Jennifer Lopez starts the chain of kindness by celebrating an inspiring young fan and her mother.

Hospital staff helped Kevin Hart recover from a serious car accident. He's back to return the favor -- and to encourage the staff to do the same.

Nick Jonas surprises longtime fan and mental health awareness advocate Carla, who in turn repays the kindness with a visit to her old high school drama teacher.

Kristen Bell shows her appreciation for a pre-school teacher who taught her a lot about motherhood.

Yara Shahidi kicks off this chain by honoring the legacy of childhood friend Cameron Boyce.

Tracy Morgan overwhelms an inspiring gym owner. Later, this community leader gets to pay it forward with an old friend.

Basketball star Anthony Davis thanks a Los Angeles local graffiti artist for welcoming him to the city when he was traded to the Lakers.

Karlie Kloss surprises a former student of her Kode With Klossy camp. And this proud pupil has another mentor she'd like to thank.

When Gabriel Iglesias was in high school, speech teacher June helped him overcome some serious issues. Now she's at a taping of his show - and in for a big surprise.