Professor Alexander Trese is the father of Anton Trese and a prominent paranormal investigator of his time.
The earliest dated mention of him is his participation in the Battle of Manila, a month long battle fought by the United States and the Philippines against Japanese troops invading the city in 1945. During it, he met the Green-Eyed Sister.
During his adventures, he kept a journal of important things that he and his family have done. These include making accidental contact with a diwata in Balete Drive, setting up eldritch checkpoints to detect Buhay na Bato around the city, and stopping a brothel run by Oriol in Makati with the help of Captain German and his police.
At some point Alexander attempted to study the activities of the Bangungot yet he failed to ascertain the exact process by which they picked the intended recipients of their 'aid'.
He also stayed with Señor Armanaz's tikbalang tribe in Bukidnon when they were discovered by a group of hunters. Armed with anting-anting that granted them invisibility, they successfully hunted the tikbalang for their body parts. The events later came to be known as the Bukidnon Massacre. In response, he and the Trese family helped Armanaz in tracking the hunters, earning Armanaz's respect. Since then, the tikbalang have helped him and his family in implementing The Agreements.
Anton and Miranda
Anton and Alexander put a stop to the Theater of Doom, freeing a pair of female aswang that were forced to fight each other for show. The aswang bore theater masks that controlled their bloodlust, manifesting every time they were in battle. The aswang remained loyal to him, serving as his personal bodyguards. Eventually, the aswang died protecting Alexander from the Maligno Horde.
Alexander accompanied Anton, Miranda, Amang Paso and Puti when they visited Anton's patient. Puti attacked a creature below the stairs and got gravely injured. The patient psychologically manifested wraiths that attacked them, and were impervious to magical attacks. Amang Paso, unaffected by the wraiths, guided them to safety.
Alexandra and the Kambal
Anton and Miranda eventually had six children that fulfilled the prophecies of the Seven Seers. The second child, Enrique, followed in Alexander's footsteps as a professor. The fifth child was stillborn when she was born with her sister, Alexandra Trese, who was named after Alexander. Alexander had the fastest tikbalang carry the child's body to the Metalero where, assisted by the Babaylan of Makiling, she was made into a kris named the Sinag.
Alexander helped Alexandra train for her responsibilities as she was prophesied to be the next Babaylan-Mandirigma,. This included bringing her to Coach Gabriel, under which she sparred with the young Manuel.
When Alexandra went inside the Great Balete Tree Trials to undergo the Great Balete Tree Trials on her eighteenth birthday, Alexander helped Anton and his sons defend the tree from four rebel clans of aswang. During the fight, Anton asked the Kambal to prioritize Alexander first instead of himself. As a last resort, Anton sacrificed himself to cast a protective spell around the Great Balete Tree, ending the fight.