Who is Gabe (the delusion) from Next to Normal and what is their importance?

Gabe first appears as a healthy, attractive eighteen year old, energized and happy to be alive. As the narrative quickly reveals, however, Gabe actually died when he was an infant (see "Gabe, The Reality," below). His manifestation in the musical, therefore, is an act of theatricalized, externalized imagination; he is both what Diana would like him to be and what Diana is afraid of, in his occasional diversions into hinting of suicide, of having control over her, and of a lingering, deathly darkness. As the narrative progresses, however, it seems clear that all this spirit of Gabe actually wants is to be remembered, to not be forgotten. As the musical concludes he, like the other principal characters, have embraced the possibility of hope, or hope of possibility. His father has begun to remember him, his mother has begun to work through her grief, and his sister has begun to realize that she truly does have an identity, a sense of self, that isn't solely defined by her relationship to him.