Nothing is known about how Dickens came to be owned by Emily Lake, though there is some speculation by fans that perhaps one of the Regents gave him to her as a way to ease the transition into life as Emily Lake. As Emily was an English teacher, it is not a stretch to assume that Dickens was named after famous author Charles Dickens.
During the fight between Pete and Marcus Diamond wherein Marcus was trying to kidnap Emily, Dickens yowled at Marcus and possibly tried to scratch him, distracting Marcus enough for Pete to gain a momentary upper hand. This caused Pete to defend Dickens to H.G., saying that he was "solid" and "saved [his] bacon".
It is unknown what happened to Dickens after Emily was taken by Walter Sykes.