Analysis of information sources in references of the Wikipedia article "Che (interjection)" in English language version.
[...] the word 'che' - meaning something like 'mate' or 'buddy'. It is used casually to grab the attention of a familiar friend, but develops an edge of impertinence if said to a figure of authority.
The Cubans were amused by Guevara's characteristically Argentine speech, peppered with the word 'che' [...]. Guevara used it to everyone. The Cubans called him 'el Che'. It stuck.