Not very much is known about his background, but he is a shy homeless man. He is known to not say very much, hence the name "Hush". He is a man in his mid forties and is good friends with the homeless poet Double-T (a veteran suffering from shell shock). Possibly he may have been a veteran too, but the reason he is homeless in unknown.
He often sleeps at the Fort Greene Men's Shelter and doesn't come out until the morning. This was where Rob Baker and Lisa Norburt learned about his existence through means of the shelter's security Guard. First they tried to speak to him, but he was shy and cold and just ran away from them.
Then Rob tried writing him a letter, this was to explain to him that he was Double-T's friend. Also that he was trying to find him because he believed he was missing. But surely enough, he didn't care so he crumpled up the letter and threw it back to the security guard.
Then finally Lisa wrote him a new letter. The letter explained who they both were, and that she was Double-T's daughter. Also that they were trying to find her dad believing he was missing and in serious danger. Then to really convince him, she guilt tripped him. She told him that if he really cared about her dad, then he will help him them.
Finally, he reluctantly decided to speak to them. At first he was cold and impatient and about to run off. Then when they begged him and he saw how concerned they were he warmed up to them. He then told them that he and Double-T used to sleep in end of an abandoned subway tunnel. He told them that the tunnel entrance they used was recently closed off by the city. Then a week prior, he found another entrance, but didn't get a chance to tell him yet.
Then when they suggested to him that perhaps Double-T may have found it himself, they asked him where it was. He told them that new entrance was over by Ebbets Field apartments. This area was formally known as the old Brooklyn Dodger Stadium. He also informed them both that the Dodgers played baseball in Brooklyn a long time ago. Then he gave them the directions and telling them walk through and then to go through a crawlspace marked "S32" and he advised them both to be very careful.
Then Rob and Lisa took his advice and followed his instructions and went down into the tunnel. Then soon enough, they and got trapped in a cave in and nearly died. He may have inadvertently led them both to a perilous adventure. Or he didn't actually think they would both go down there. Or possibly he isn't a very safe homeless person to associate with, and he may have some serious mental issues. Although neither possibility was directly addressed in the series.