In folklore, a lycanthrope is person who through a curse, magic, or other means, has the ability or is forced to transform into an animal for a period of time. The term comes from ancient Greek lykanthropos: lykos ("wolf") + anthropos ("man"). Originally, the term lycanthrope meant only the specific species of werewolf, however, it has grown to encompass any person who can shapeshift into an animal

There is also a mental illness called lycanthropy in which a patient believes he/she is transformed into an animal and behaves accordingly, sometimes referred to as clinical lycanthropy to distinguish it from legend. These individuals undergo a complete change of personalty, from a normal and rational mindset into a savage and irrational one, often acting like threatened wild animals, attacking any who approach with clawing and bites. The sufferer apparently has no control over this change in personality, and so it is both dangerous to himself/herself as well as those around him/her.

Last but not least, therians who claim to have the wolf as their wereside call themselves werewolves or lycaons.