Most Dota 2 heroes were originally ported from the original DotA (Defense of the Ancients) Allstars mod in Warcraft 3. However, after TI6 Valve has started to create their own original heroes.
Monkey King was the first original Dota 2 hero, as the hero was heavily inspired by the tales of Sun Wukong.
Pangolier was revealed at TI7, as part of the Dueling Fates update along with Dark Willow.
Dark Willow was released on the same date as Pangolier, as she was a part of the Dueling Fates update.
Grimstroke was next, as he was revealed at TI8 alongside Mars.
Despite being the son of Zeus in the Dota 2 universe, Mars is named after the Roman god of war, instead of the Greek equivalent, Ares.
Void Spirit is revealed as the 4th celestial at TI9, with Ember Spirit , Storm Spirit & Earth Spirit being the other three.