Thundra was far from obscure in ‘70s Marvel comics - she was everywhere for awhile there. Created during the feminist movement, she was probably Marvel’s first truly strong (in a physical sense) female character. She may have been Marvel’s answer to Wonder Woman by way of Big Barda. A time traveller from the 23rd century, Thundra comes from a future where Earth is renamed “Femizonia”, and the United States is renamed the “United Sisterhood Republic. Also, manacles are now called femicles, manatees are womanatees, and the very richest, most sucessful women live in m’aam-sions.*
She initially came to present-day Earth to beat the Thing (mistakenly identified to her as the strongest man on Earth) in hand to hand combat to demonstrate female superiority. Instead, she fell in love with the rocky man-brute, and stayed around for a few years pursuing him. Eventually, she settled down with Arkon, a thunderbolt-hurling, otherdimensional barbarian-type character, and left our era to join him on his homeworld Polemachus. As far as I know, both were last seen being wiped out by Krona in JLA/Avengers, but that may not “count”, as it was an intercompany crossover, and probably not canon. She’ll be back.
*I'm so sorry.