Ben is the most well-rounded character in It (no pun intended.) His being fat earns his place in the Loser's Club, but like all of the Losers, there are underlying facets that define him far more than his weight.

At the beginning of his "young" stage in 1958, Ben is a shy, bookish boy with no friends. He has an attatchment to his mother and other adults, who adore him because he is a "good boy." His only relationships come with adults: he goes so far as to volunteer to help Miss Douglas catalogue books when the other children go home. He also has a crush on a girl in his class named Beverly Marsh -- he looks past the rich girls in the glass and centers on the poor girl with the bruise on her face. Perhaps on a deep, unknown level he sees a certain desperation for companionship in her, as well. In a bold move that seems to be the first step he takes to achieving friends on his own, he writes Beverly a poem:

and mails it to her. This act of reaching out for companionship is one of the first steps taken to infuse the Loser's club as a whole.

That day, while being cut by Henry Bowers (the fact that Henry decides to carve on Ben's stomach rather than his arms or face is significant), Ben breaks out of his character even further -- fighting back, kicking Bowers in the crotch, and tumbling down the hill into the Barrens where, later, he meets Bill and Eddie.

Ben stays with Eddie while Bill goes to get Eddie's asthma medicine, and the fact that he doesn't run off is another strengthening bond. By his nature, he is afraid and alone. But escaping from the Mummy earlier that year and escaping from Bowers that day toughened him. As Beverly later observes: "Ben may have been nothing but a frightened fat kid at the beginning of the summer, but he was stronger now; they all were." Bill also thinks of Ben as tougher than Richie and less likely to break down suddenly than Stan.

Then there is his talent for building things. The first group effort, the building of the dam in the Barrens, even shuts Richie up for awhile. His production of the Smoke-Hole allows Mike and Richie the vision of It's arrival to earth, and his forming the silver slugs later helps save his own life. These three incidents, the dam, the Smoke-Hole ceremony, and the battle at Neibolt Street, are three of the most significant sequences in the book, all made possible by Ben Hanscom. It is apparent that he is one of the most important members of the Loser's Club; his knack for creation could only flourish through his acceptance into freindship.

He is also the most sensitive and, in many ways, the most thoughtful of the club. He recognizes Bill's leadership in the group, accepts it, and knows that Bev is in love with him. He allows that in his mind, and in his heart, knowing that he could have Bev as a friend and love her silently. Everyone else seems to recognize the love Ben feels for Beverly except Bev herself, until the day of the final confrontation. The exchange between Bev and Ben in the Smoke-Hole after her escape from her father and Bowers & co. is perhaps the most sensitive and sweet conversations in all of King's work. People that say he just writes horror and cares only about blood and guts should get a load of this:

"Thank you for the poem, Ben."
"Poem?"
"The haiku. The haiku on the postcard. You sent it, didn't you?"
"No. I didn't send you any haiku. Cause if a kid like me -- a fat kid like me -- did something like that, the girl would probably laugh at him."
"I didn't laugh. I thought it was beautiful."
"I could never write anything beautiful. Bill, maybe. Not me."
"Bill will [...] never write anything as nice as that."
[abridging, here]
He was even able to look at her as he said it.
"I wrote the poem."

This conversation allows Bev and Ben to form a deeper bond with each other, allowing more tenderness in the later love scenes than any of the Losers can give her. Bill makes her skyrocket, both in the tunnels and later at the Derry Town House, but Ben fills her with love and desire, and that is the reason why she goes home with Ben at the end.

On a final note, perhaps Ben comes the closest to discovering the true nature of the Loser's Club and the forces that guide them. During a quiet moment, he wonders about power, where it comes from and where it goes. The power of the slugs, the power the Losers have to defeat It and Bowers time after time. Did the power simply come from them, or was a higher force at work? It is in this unarticulated musing Ben has with himself that defines the entire novel.

He realizes that power comes from everywhere, but the greatest of these sources is the influence of love. He recognizes that Bill has power over Bev because she loves him, and that she has power over him because he loves her. Collectively (and, yes, it is Ben who mentions this 27 years later, at the library) the Loser's Club all love each other, a binding love that overcomes amnesia and death. And somewhere, some Other is looking down on them with love, as well.

In closing, Ben Hanscom comes to maybe the most complete closure. At the beginning of the novel, both as an adult at the bar and as a kid on the last day of school, he is a lonely boy with no friends, and he is in love with Bev Marsh/Rogan. In 1958, he stands up for Beverly, feeling an overpowering need to protect her (my guess is if It hadn't gotten Tom, Ben would have probably done a job on him.) And after he finally confesses his love to her, and goes the further step of making love with her, he loses her. After twenty-seven years (and around two hundred pounds), he catches her again, and this time holds on.

Not bad for a lonely fat kid who's handy with Lincoln Logs, huh?