Another citizen of the weird town that is Locksmouth, Simon is a creative boy who's much better with instruments than people. Unlike Shelly, his SDD was diagnosed at an early age and the tweenager's friends are generally very supportive of him, allowing him to participate passively in conversations and enjoy more physical affections like hugs and high-fives. He's a big music lover, and if you're a stranger, you're much more likely to see him play one of his many musical implements than try to hold a conversation.
That said, Locksmouth is a weird town; could that really be all there is to him...?