Who is John Harmon from Our Mutual Friend and what is their importance?

John Harmon is the heir of the Harmon estate, as long as he marries a girl named Bella Wilfer. However, he is presumed to be dead when a man wearing his clothes and with his possessions is found in the River Thames. Harmon, however, actually assumes the identity of John Rokesmith and initially obtains a room at the Wilfer household. He latter attains a position as Noddy Boffin's secretary, allowing him to get to know Bella Wilfer, who has become the ward of the Boffins.