[nandemo]

"Buddy" sounds really silly. "Comrade" is closer, but at least in Portuguese that would be "camarada", which carries a rather old-style socialist nuance, not "companheiro".

"Fellow", "brother" or even "mate" sound better in this context.

[JVIDEL]

Indeed the word is "companero", but its not as formal as comrade which also exists as "camarada", in this context its actually more like partner (in a professional sense) but not as informal as brother or pal in english.

Peron put that word en vogue around here.