Who is Daniel Williamson from Reminiscences of a Stock Operator and what is their importance?

Daniel Williamson is the proprietor of Williamson & Brown, a brokerage in New York, which mostly has a few large customers. Williamson convinces Livingston to sign on at a time when Livingston is flat broke due to his cotton deals, by providing him with a stake and a brokerage account. Williamson wants Livingston to join the firm to obscure the activities of his other traders so the market cannot guess what they are up to. Williamson is very kind and continues to cover Livingston's losses, but never explains where the money is coming from and sometimes advises him to take actions that are against Livingston's natural trading inclinations.