Mr. Sullivan stands as the primary antagonist in the series' first season, occupying the role of director at the Bank of England and holding prominence within London's Reform Club. A longstanding rivalry with fellow member Willy Fog fuels their central conflict.

Sullivan initiates a wager against Fog, betting £5,000 that Fog cannot complete a global circumnavigation within eighty days. Additional bets from other club members elevate the total stake to £20,000. To ensure Fog’s failure, Sullivan orchestrates a £55,000 robbery at his own bank and secretly hires a mercenary saboteur named Transfer. Transfer impedes Fog through deliberate misdirection, engineered transportation accidents, and actions that endanger lives.

Sullivan’s personality merges surface professionalism with deep vindictiveness. Publicly, he maintains a stern, composed demeanor, initially expressing confidence in his employees' innocence after the heist. Privately, he harbors intense envy toward Fog, ridiculing his ambitions and voicing hopes for his demise during the journey. Sullivan’s actions stem from a desire to prevent Fog from achieving heroic status and winning the wager.

Following Fog’s successful return to London and exoneration from robbery accusations, Sullivan is compelled to honor the bet’s financial terms. The journey’s conclusion results in his dismissal as bank director, marking his professional downfall.

No concrete information exists regarding Sullivan’s origins or life prior to banking. His full name remains unspecified, though indirect references suggest a possible connection to "John Sullivan" from Jules Verne’s original novel; this link remains unconfirmed within the series’ canon.

The character does not appear or receive development in subsequent seasons, films, or spin-off media. His narrative arc concludes exclusively within the first season.