Who is Henry from Next to Normal and what is their importance?

Henry is a little older than Natalie, but they go to the same school. He is described in stage directions as a "musician. Romantic. Stoner. Slacker. Philosopher king." He is, in spite of his apparently frequent drug use, easily the wisest, most grounded, most realistic character in the whole musical. He is also more genuine and more constant in his love than Dan, more alive and more empathetic than Gabe but at least as insistent and, while somewhat unstable, is ultimately far more together than Diana. His persistent and honest affection for Natalie finally breaks down her resistance, and she finally agrees to attend a high school dance with him, a trigger for both of them to join in the show's final song celebrating the power of hope and possibility as symbolized by light.