He was described as wealthy, sporting gilt spurs and a rich woolen cloak. He was also fluent in French.
Trumper-Jones served as Sharpe's advocate during his court martial for murder. He suggested that the case for Sharpe look bleak, that they might present Sharpe's record to the court. "You want me to plead guilty and hope they won't shoot a hero, is that it?" Sharpe then ignored Trumper-Jones and wrote his suspicions of a plot out in letter to Hogan, directing that it should be handed to Hogan even if he were dead.
When a court-martial found Sharpe guilty of murder, Trumper-Jones made a notably impassioned speech for the prisoner, citing his many instances of gallantry, his heroism, his devotion to duty, and contribution to England's cause, and futilely begged the court for leniency.
Between the two meetings, Sharpe had all but forgotten the first encounter with Trumper-Jones, and when they met again, he asked if he had met the younger man's father, as he remembered a cavalry officer called Trumper-Jones who had lost an arm and an eye at Rolica
In the television movie, Sharpe's Honour, Trumper-Jones wore the coat of an infantryman rather than a cavalry officer.