And it should have positive connotations and it should be a noun
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I have no attribution for this in writing; but, it was the term my father used for those whom he admired for their steadfastness, and refusal to simply go along with the tide. In every instance, the one referred-to had made a substantial contribution to humanity by contribution or by setting an example.
To me, it has come to mean a high compliment
You might call this person unique:
being the only one of its kind; unlike anything else.
"the situation was unique in modern politics"
synonyms: distinctive, distinct, individual, special, idiosyncratic; single, sole, lone, unrepeated, unrepeatable, solitary, exclusive, rare, uncommon, unusual, sui generis;
informal: one-off, one-of-a-kind, once-in-a-lifetime, one-shot
"each site is unique"
Edit: You've edited your question to request a noun. You might consider maverick or one of its synonyms:
an unorthodox or independent-minded person.
"a maverick among Connecticut Republicans"
synonyms: individualist, nonconformist, free spirit, unorthodox person, original, eccentric; rebel, dissenter, dissident, enfant terrible;
informal: cowboy, loose cannon, bad boy
"he was the maverick in the family, the only one who valued freedom over an inheritance"