Haoji, also known as Oslo, once reigned as King of All Food before his student, King Gorgeous Gorge, betrayed him. This treachery reduced Haoji to miniature size, forcing him to rely on a floating saucer for movement.

Transformed, he embraced the role of Grub Guru, mentoring aspiring chefs. He first trained Chef Jack, the Master Chef leading the Rebel Chefs against the Glutton Empire. Later, he focused on guiding Jack's son, Chase, towards Master Chef status to oppose King Gorge. Haoji trained Chase in creating and wielding Foodons for culinary combat.

Possessing vast knowledge of Foodon lore and culinary magic, Haoji's physical limitations prevent him from fighting directly. He instead offers crucial tactical support during clashes with the Glutton Empire. His expertise proves vital, enabling Chase to summon Palator, the embodiment of good, to counter King Gorge's Devouron in the final conflict. This act facilitates Gorge's redemption and the empire's downfall.

Flashbacks reveal a younger Haoji, contrasting sharply with his current form and highlighting the betrayal's impact. His journey focuses on resilience and mentorship, evolving from a deposed monarch to a key resistance figure. Following victory, he continues supporting culinary traditions without reclaiming his former title.