Argus Steel is a professional thief specializing in stealth, deploying advanced technology like an invisible airship to track targets and conduct undetected surveillance. His primary objective was pursuing the mythical Pokémon Diancie to exploit its diamond-creating ability for personal profit. He operated alongside his daughter, Millis Steel, their partnership extending to monitoring rival thieves Merilyn Flame and Ninja Riot during the Diancie pursuit.

He exhibits a significant preoccupation with chocolate, consuming it excessively during missions despite Millis's expressed health concerns. This preference later shaped his post-criminal career choice. During the climax within Allearth Forest, he shielded Millis from Yveltal's Oblivion Wing attack, resulting in both being petrified. They were subsequently revived by Xerneas's Geomancy. Following this, he abandoned crime and transitioned to operating a chocolate shop with Millis, though he continued demonstrating difficulty resisting chocolate consumption during their business.

His known Pokémon include:
- Honedge: Primarily deployed for covert surveillance operations against Diancie.
- Doublade: Typically utilized by Millis for aerial transportation.
- Aegislash: Served as his primary battle Pokémon, capable of carrying him during ground movement.

His character design reflects visual similarities to Honedge's aesthetic. After his redemption, he maintained his chocolate-focused lifestyle within the legitimate business. His activities are documented within the Kalos region.