Animated skeletons, along with the Grim Reaper, have been used as personifications of death since the Middle Ages, a personification perhaps influenced by the valley of the dry bones in the Biblical Book of Ezekiel. Skeletons are commonly depicted as beings of evil or death during celebrations and holidays such as Halloween and the Day of the Dead.
In popular culture, skeletons commonly serve as villainous characters due to their dark nature and connections to death. This includes animated skeletons being used as minions to more powerful villains (usually necromancers or other types of magic users) and more powerful undead and skeletal entities (such as liches). Skeletons are also used as common theming by villains to represent their deadly abilities; some dress as skeletons or use them as symbols or emblems of their character or organization.
In modern times, skeletons are also commonly associated with scaring and horror, being one of the universal icons for the holiday of Halloween, and have been used in decorations, media, and memes regarding the holiday.
Additionally, while human skeletons are commonly used, other animals such as horses, bulls, rams, rats, and more are often used in similar fashions, and may be used as pets or steeds of the human skeletons.