Upright
Stable, successful person. Success in material or business matters.
The King of Pentacles
The visionary with a plan.
Reversed
Corruption, greed, winning at all costs.
Kings can represent influences, or more commonly, people. In both cases, the King of Pentacles is a herald of success.
As a person, the King is stable and successful. This is a ruling visionary, someone in a person of power, who always has a solid plan. If the Queen of Pentacles suggests successful navigation of the social and societal sphere, the King represents navigation of the material world: finances, business, houses, craft, and more. As an influence, the King brings success in material matters or business. It indicates loyalty and resolutions.
When reversed, the King may represent someone with these qualities who is negatively influencing the querent. It may also suggest someone (perhaps the querent) is exhibiting the qualities of the King on a particularly bad day: corrupt, greedy, and ambitious, this King may try to win at all costs.