Theresa "Tessa" Gray was an American warlock.
- This character's history and characteristics are identical to that of her alternate dimension counterpart up until just before the Dark War, where the timeline split and the following changes took place.
After the Dark War ended and Sebastian Morgenstern continued his conquest of the world by spreading the blight, the warlocks began to sicken. Tessa was immune to the sickness due to her Shadowhunter heritage, and attempted to help her fellow warlocks, but despite the discovery of Lake Lyn water as a potential cure, they quickly grew worse and eventually turned into demons themselves, leaving Tessa as the last warlock on earth. At some point over the next seven years Tessa, alone after the death of Brother Zachariah, went into hiding in Los Angeles, living in a cave on the coastline.
In 2014, after receiving a message from Emma Carstairs who had traveled to Thule with Julian Blackthorn, Tessa sent Church, who had been living with her, to find and retrieve them. She met with them at the beach, appearing as Brother Zachariah to gauge their reaction, as she knew that Emma would be happy to see him while anyone who was allied with Sebastian would be horrified to see a Silent Brother. Tessa recognized them to be from another world because as a warlock she could see into other worlds, just as she saw into theirs.
Inside her cave, Tessa explained more of what had happened to her world, revealing that the waters of Lake Lyn could cure the warlock sickness and end the blight. She also explained how the Silent Brothers had died sealing the Silent City and the Mortal Instruments to keep them safe from Sebastian until someone could use them to kill them. She agreed to help Emma and Julian break the seal and retrieve the Mortal Sword, so they could kill Sebastian.
They met up once again when Tessa opened the doors of the Silent City for Emma, Julian and the rebels to retrieve the Mortal Sword and Cup of Thule. Once they had retrieved the sword and the cup, the Endarkened, led by Sebastian, invaded the Silent City and attacked the rebels. After fighting with the Endarkened, the rebels escaped the Silent City and Tessa, already weakened from her use of magic, closed the doors, leaving Cameron Ashdown trapped inside. Shortly afterward, Tessa burst into flames, becoming a pillar of fire and dying.
- Queen of Air and Darkness (first and only appearance)