«THE SWORDSMAN OF MARS & Its Sequel, The Outlaws of Mars» by Otis Adelbert Kline

“The Swordsman of Mars” is a story of Harry Thorne, an outcast descendent of a noble family, in search for the grand adventure. He swaps bodies with a young hot-headed Martian Sheb Takkor, and gets transported to Mars, many years into the past. He arrives to a pulsating planet inhabited with scary beasts and creatures, fierce warriors, and beautiful and dangerous women, where he must confront various challenges in order to fulfill his destiny of a swordsman.
“The Outlaws of Mars” is a continuation of a Mars series, this time with Jerry Morgan, a man with no future on Earth, who gets offered a new life on Mars. He starts out on the wrong foot, meeting a princess Junia and killing the fearsome-looking Martian beast he takes to be menacing her, which actually turns out to be her pet. After being imprisoned, Morgan becomes entangled in the politics of the Byzantine Martian royal court. Various adventures follow, with dazzling swordplay, feats of strength, and other trials, tribulations and treacheries.
Otis Adelbert Kline was an adventure and science-fiction novelist, best known for his interplanetary adventure novels set on Venus and Mars, which instantly became science-fiction classics.