The main character of “The Whale” is 600 pounds, but one of the many pleasures of this funny and affecting new play by Samuel D. Hunter, being given a splendid production with a universally first-rate cast at Playwrights Horizons, is the realization that the title, like the play itself, turns out to be about much more than just Charlie’s morbid obesity.

At first we only see this huge man – played exquisitely by Broadway veteran Shuler Hensley – so hobbled by his own gluttony that he is literally killing himself. We are given to understand that Charlie, living alone in a smelly apartment in Idaho, is unlikely to last the week. (The play begins with Monday projected onto the wall, and goes day by day through Friday.) Yet he refuses to go to a hospital.

But it does not take long before we get to know him and the people around him – his exasperated nurse Liz; his cruel and angry teenage daughter Ellie whom he hasn’t since she was two years old, and offers to pay to visit him; his hard-drinking ex-wife Mary; and a seemingly random visitor to Charlie’s apartment, a young man on a Mormon mission. All prove to be more complex and more sympathetic than first impressions.

Charlie makes a living teaching expository writing online — an occupation that allows for great moments of hilarity as he assesses the students’ essays. It also gives the playwright sly and unobtrusive ways to introduce resonant themes….including those contained in both Moby Dick and Jonah and the Whale…which have a pay-off at the end.

Hunter, the author of the much-praised “A Bright New Boise,” offers a play that is full of moments of revelation that unfold with impressive craftsmanship.  There are big revelations: Charlie began to eat obsessively when his partner Alan – the man for whom Charlie left his family – suddenly stopped eating and wasted away, in effect starving himself to death, after a visit from his father, a bishop in the Mormon Church.  One or two of the revelations are perhaps too pat, such as a lie that  daughter Ellie unearths that Elder Thomas has been telling. But most of the revelations are simultaneously subtle and astonishing.  There is a richness here of characterization and interaction, helped along by wonderful performances,  that reveal in the tiniest details a playwright whose heart is gargantuan.