Loner

A loner is a person who avoids or does not actively seek human interaction. There are many reasons for solitude, intentional or otherwise. Intentional reasons include being introverted, spiritual, mystic and religious considerations or personal philosophies. Unintentional reasons involve being highly sensitive, extremely shy, past trauma or events, or having various mental disorders.

The term "loner" can be used with a negative connotation in the belief that human beings are social creatures and those that do not participate are deviant. Being a loner is sometimes depicted culturally as a positive personality trait, as indicative of being independent and responsible.

There are different types of loner, including individuals that prefer solitude and are content to have very limited social interaction. The second type includes individuals that are forced to be isolated because they are rejected by society. This individual typically experiences loneliness. Another type is an individual that is social, likes to be social, and has lots of social interactions but prefers solitude without feeling lonely. The first type often does not feel lonely even when they are alone, at least, not in the same way as would a social person who found themselves isolated. However, these are very broad generalizations and it is not uncommon for loners to experience both of these dimensions at some point. Being a loner can sometimes be a symptom of certain mental illnesses such as depression, schizophrenia, and autism. People with autism, for instance, have difficulty with social interactions and limited or restrictive interests and routines which would make it more likely for the person to be a loner.

...
Wikipedia