Modifiers matching grump:

• covetous,
• greedy,
• rich,
• mean,
• grouchy,
• ill-tempered,
• condescending,
• penny-pinching,
• misanthropic,
• impatient,
• miserly,
• gruff,
• arrogant,
• grizzled,
• heartless,
• wealthy,
• fastidious,
• principled,
• jealous,

Simple categories matching heartless:

• tyrant,
• person,
• robot,
• demon,
• warrior,
• criminal,
• terrorist,
• conqueror,
• tycoon,
• dictator,
• psychopath,
• miser,
• bully,
• vampire,
• villain,
• thug,
• killer,
• businessman,
• thief,
• grump,