It also serves as a building block for William's creatures, including the Rougarou and his two servants, Sinister and Heavy. When it is not being used, it takes the form of a ball of 'black goo' and covers the hand of the user when crushed.
From what is known, Mara and William brought Aether to Haven about 500 years ago and used it to give people troubles. In William they are first seen going into people and giving them hallucinations. Gloria discovered the aether during autopsies on some victims and revealed what she had discovered to Audrey. In When the Bough Breaks William gives Audrey some Aether to give someone a trouble.
In See No Evil, Mara is looking for William's Stash of Aether hidden in Haven. In Speak No Evil Mara finds out there is some aether in the morgue, but Gloria hides it from her. Gloria gives it to Nathan, who uses it as a bargaining chip against Mara. He gives an aether to Mara and she splits it and puts half in her pocket.
In Chosen, Duke is able to create aether from his body thanks to Mara using aether on him to create this ability.
In "Power", Charlotte tells Nathan she believes she can cure the troubles using Aether. Nathan heads out with Kira Fulcher to find it using Seth's detector he left behind. Nathan finds William's hidden stash of Aether hidden in a cavern. In "The Trial of Nathan Wuornos", Kira Fulcher becomes trapped in the cavern and Nathan sends Dwight and Charlotte to find her and the Aether. When they find it, Charlotte mentions it won't be enough to end the troubles, but they find a room beside it filled with much more Aether.
In Wild Card, Audrey and Charlotte condense the Aether in William's hidden cache into a ball in order to create a new Barn to cure the troubles. In A Matter of Time, William convinces Nathan to give him some pure aether so they could "escape" but instead uses it to recreate Heavy. In Blind Spot, Audrey is trying to figure out how to create a new barn with the Aether core and controller. The Aether core is later damaged by Duke Crocker.
In The Widening Gyre, Croatoan reveals to Audrey that he used aether on Mara to save her life. In Now, Nathan and Audrey try to repair the Aether core using Vickie's trouble but are foiled when Duke uses it to destroy the core. When Duke finally comes to his sense, Croatoan begins collecting the trouble from Duke. Croatoan is foiled when Nathan kills Duke in order to keep the aether inside Duke.
In Forever, Croatoan summons a rain cloud of Aether from the void in order to force Audrey to help him with his work. When Audrey does, she channels it into the Haven Armory but stops when Nathan reappears. Croatoan is angered by this and throws Aether at Audrey but Nathan is hit instead. Using the Aether inside Croatoan, they build a new barn that removes all the aether from the troubled people. In addition to closing the Aether rain cloud.