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Explanation: Just looking in my Colling Spanish-English dictionary and is gives the translation of a lone wolf as "ser un solitario", and Anaya on-line dictionary defines it as "persona solitaria". Here, the lone giving the impression of a creature/person independent, not necessarily lonely, or as Dictionary.com defines, "One who prefers to go without the company or assistance of others. Also called lone hand".
If this is the idea you're after, then choose "EL SOLITARIO" or "EL LOBO SOLITARIO" if you want to include the wolf. If don't like so much the English definition of the owrd then try one of the other suggestions on this page. I hope this helps!
Neil (English prof).