When Simon Lewis was accidentally brought to Alicante with the Lightwoods during his term, the Inquisitor expressed interest in seeing him. Assuming that the Clave merely wanted to Portal Simon back to New York, Alec voluntarily delivered Simon to him, despite Jace's doubts about the Inquisitor, due to his experience with Imogen. Aldertree, however, threw Simon in jail, hoping to force him to lie by testifying that Robert, Maryse, Alec, and Jace were in league with Valentine Morgenstern. When Simon refused, Aldertree had him put back in jail.
When Valentine showed up in the Accords Hall, Aldertree rushed over to attack him, not knowing it was merely a projection. While he was unable to touch the image and went right through it, Valentine managed to make his hand materialize inside him and was killed. After his death, the position was vacated for weeks. Appointing a new Inquisitor, and Consul, was among the priorities of the Clave after the Mortal War. Robert Lightwood put his name in for the position, and he was soon appointed.
Aldertree gave an impression of cheeriness. His deceitful nature was revealed when he locked Simon up and blackmailed him into turning the Clave against the Lightwoods. He was power-hungry, abusive of his powers as Inquisitor, arrogant, and over-confident even moments before his death.
Aldertree is short, round, and bald with a shiny head.