Ernesto Guevara is probably best known by his nickname, "Che". How did he get it?

Ernesto Guevara became known as "Che" because of his distinctive habit of frequently using the interjection "che" in conversation. In Argentina and some other South American countries, "che" is a casual expression similar to "hey" or "buddy", often used to get someone's attention or to emphasise a point.

As Guevara travelled and fought alongside Cuban revolutionaries, his Argentine background stood out because of this linguistic quirk. His comrades began calling him "Che" and the nickname stuck, eventually becoming synonymous with his identity as a revolutionary figure.

https://arsof-history.org/articles/v4n4_false_idol_page_1.html