Willy Fog is a wealthy British gentleman of unspecified origin residing at Savile Row in London, renowned for his strict adherence to punctuality and meticulous routines, including scheduled morning exercises and breakfast preparation. He leads a secluded existence with no family, primarily frequenting the elite Reform Club. Physically depicted as an anthropomorphic lion, he wears a distinctive brown suit, white shirt, red tie with black or white polka dots, a top hat, and carries a cane with a ball handle. He avoids firearms, relying instead on this cane for defense, demonstrating proficiency in "Cane Fu" to disarm opponents or deflect projectiles.

His life changes dramatically when he accepts a £20,000 wager at the Reform Club to circumnavigate the globe in 80 days, defending the honor of Lord Guinness. Despite years of sedentary life, Fog departs London immediately with his newly hired French valet Rigodon (a cat) and Rigodon's companion Tico (a small rodent-like creature). Inspector Dix and Constable Bully of Scotland Yard pursue him, mistakenly believing he robbed the Bank of England, while the saboteur Transfer, hired by Fog's rival Sullivan, actively tries to ensure his failure.

Throughout the arduous journey, Fog exhibits unwavering stoicism, maintaining composure amidst disasters, attacks, and delays. He adheres to a strong moral code, rejecting unnecessary violence and assisting those in distress, exemplified by rescuing Princess Romy (a panther) from forced suttee in India and later offering her sanctuary after her relatives' demise. His leadership unites the group during crises, such as navigating a mutiny aboard the Henrietta or countering Transfer's sabotage.

Fog's relationship with Romy evolves from protector to romantic partner. While ensuring her well-being, his reserved nature limits overt displays of affection. Upon initially missing the wager's deadline and losing his fortune, Romy proposes marriage. Fog accepts after discovering a time-zone error secured his victory, allowing them to marry and use the winnings to rebuild their lives.

In subsequent adventures exploring narratives adapted from Jules Verne, Fog journeys with Romy, Rigodon, and Tico. These tales retain his core traits: loyalty, calm problem-solving, and principled actions, whether facing subterranean dangers or oceanic perils. His development shows increased adaptability and deepened relationships, though his fundamental identity as a precise, principled gentleman endures. His actions consistently prioritize others' safety, like refusing to steal an elephant despite urgency, and his marriage signifies a measured shift toward emotional openness within his dignified demeanor.