The use of the word “handle” to mean a nickname or pseudonym originates from CB (citizens band) radio culture in the United States during the mid-20th century. CB radio users needed a way to identify themselves while maintaining some anonymity, so they adopted unique names or pseudonyms, which became known as “handles.”
The term likely derives from the general sense of the word “handle” as something you use to grasp or manipulate an object. In this context, a “handle” serves as a figurative way to “grasp” someone’s identity in a communication setting. Over time, the use of “handle” expanded into other areas, such as online communities, gaming, and social media, where it retains the same meaning as a username or alias.