Mercurians are the natives of the planet Mercuria.
Mercurians are a Near-Human race, and so appear nearly identical to Humans. They have the ability to turn into mercury.
A notable Mercurian is Tyzonn, he was previously a member of the Intergalactic Emergency Responder Squad, a search and rescue team, alongside his fiancée Vella. During an unfortunate accident when his team was killed by the Fearcats after he sent them back into a collapsing cave, Tyzonn dedicated himself to tracking down the criminal group and bringing them to justice for their crimes.
He managed to track them to Earth, but his search was cut short when he was confronted by Moltor who attacked Tyzonn in the desert and transformed him into a Pachycephalosaurus/dragon-like Lava Lizard. In exchange for his loyalty, he promised to turn him back to normal. However, Mack realized that he wasn't a villain, and the Rangers worked with him to retrieve the Parchment as well as the Touru Diamond. The power of the two Corona Aurora gems reverted him back to his humanoid form afterwards.
When the Fearcats attacked anew with extra power granted by Flurious, Tyzonn at first refused to join the other Rangers in battle due to the fear of causing the deaths of another group of friends. However, thanks to Ronny convincing him that his past experiences weren't his fault, he was able to move on, and took the powers of the Mercury Ranger to combat the Fearcats alongside his new team. He's had some problems adjusting to life on Earth - in Just Like Me he annoyed Will by trying too hard to be like him. He's shown an interest in learning more about his teammates, trying hard to find out about Rose in One Fine Day. He grows a plant in his spare time.
He confided in the Rangers about his Vella's death at the hands of the Fearcat Crazar. This was proven false in Home and Away - after Tyzonn was injured by Kamdor in battle, Crazar set up a dream-like reality around her and replicated Vella's form, trying to make him believe everything had been a dream so he wouldn't interfere with the Fearcat's plans. After seeing through the disguise, he learnt that Vella was still alive (as she couldn't be replicated otherwise). He destroyed Crazar in a vicious battle before assisting the Rangers in their final battle against the Fearcats, personally taking out Mig as well. With his original mission over, he vowed that once the Corona Aurora was safe he would search for Vella. (Red Ranger Unplugged)
Following the defeat of the Overdrive Rangers' remaining enemies and Mack's transformation into a human being by the Corona Aurora, Tyzonn finally got his reunion with Vella thanks to Norg.