Daniel Holtz's History
The 18th century
Holtz was a vampire hunter from England who started slaying vampires from 1754. At one point, he lived in York, but Connor's references to "white cliffs" suggested he may originally be from the South-East of England rather than the North-East, either from Dover in Kent, or near the "Seven Sisters" in Sussex. Holtz chased the vampires Angelus and Darla through much of Europe and North Africa. In his nine years pursing them, Holtz killed a total of 378 vampires.
In May 1764, Angelus and Darla gained entrance into Holtz's home and attacked his family, killing his wife along with their infant son, and siring his daughter, Sarah. Upon returning home, Holtz threw his undead daughter into direct sunlight and watched her burn into ashes.
In 1765, Holtz tracked Angelus and Darla in Italy. The vampires fled to Arles, France but were eventually trapped inside a burning barn thanks to Holtz. Darla escaped on their only horse and left Angelus to fend for himself.
In 1767 the vampire James burned down the villa of the Count de Leon, much to the anger of Angelus as this brought them to the attention of Holtz who tracked them in Marseilles, France. Despite a confrontation with the two vampires aided by a large group of men armed with crossbows and riding on horseback, Angelus attempted to save his own life by revealing the location of Darla and James' beau Elisabeth. Holtz preceded to have his men kill them, but both Angelus and James escaped with the former being only wounded from an arrow.
In 1771 Holtz finally managed to trap Angelus in the sewers beneath Rome with the help of the excommunicated Archbishop Monseigneur Rivalli (who also performed his wedding ceremony with his wife Caroline) along with his order of inquisitors. Holtz tortured Angelus for hours; but eventually Darla arrived and broke him free. They left Holtz behind and chose not to kill him as they now considered him "like family." Following this incident, Holtz gave up his hunt and became a hermit.
In 1773, the demon Sahjhan appeared before Holtz and offered him a chance at revenge, revealing to him it would be his only opportunity to avenge his family as he would die of old age otherwise. He only asked in return that Holtz gave him his word that when the time came, he would show no mercy. Holtz, even though hostile at first, accepted the offer on those terms.
Los Angeles
Holtz was placed in a state of mystical suspended animation, and was reawakened in Los Angeles in the year 2001. Despite having been in suspension for over two hundred years, Holtz was immediately ready and willing to kill Angelus, with no need of physical recovery. He was briefed by Sahjhan on navigating the city and how the world had changed in the last centuries, showing him important historical events on multiple televisions.
Holtz was also given a new army, this time a cadre of Grappler demons. However, a lot had changed in those 200 years: Darla was pregnant, Angelus now had a soul and was now known as Angel. With his new minions, Holtz took out a SWAT team hired by Wolfram & Hart at the Hyperion Hotel and held Angel at his mercy. Angel tried to tell Holtz he was good now but he wasn't convinced until Wolfram & Hart's Lilah Morgan intervened and explained it to him. Realizing this, Holtz thought it was more justly to kill him and end his eternal torment. Angel then escaped by setting off a grenade and blowing himself out of there.
As Angel, Darla and his friends then vacated to the demon friendly bar Caritas, Holtz destroyed it by rolling an explosive barrel into the building, not provoking the no-violence spell as he was not presently causing any harm within the bar. He then proceeded into the flaming ruins armed with a crossbow after Angel. However, he stopped at the sight of Angel's newborn son Connor. Since his motives were not in the interest of justice but rather vengeance, Holtz spared Angel's life — unsatisfied with merely killing him — and began to target those Angel cared about in order to cause the vampire as much pain as he had caused him.
Holtz poisoned his demon mercenaries for being soulless soldiers of fortune. Holtz wanted real warriors, people who believed in his cause and would be ready to die for it. His first recruit was a brash young vampire hunter, Justine Cooper, who had lost her twin sister to a vampire attack and had since fallen to drinking and wandering graveyards at nights hunting vampires. Holtz manipulated her thirst for vengeance, as well as that of many others, and built an army of like-minded individuals.
Shortly after Connor's birth, Holtz arranged, with help from Aubrey Jenkins as part of his vendetta against Angel, for Gunn and Fred to be ambushed by a vampire's nest — something the 18th century Holtz would have sought to eradicate immediately. This ambush failed, but he subsequently convinced Wesley Wyndam-Pryce, who believed a false prophecy that announced Angel would kill his own child, to kidnap Connor. Out of devotion to Holtz, Justine helped abduct the baby and slit Wesley's throat.
Holtz and Justine planned on keeping Connor for themselves and raise him as their own at a small ranch in Utah, even renaming him as Steven Franklin Thomas Holtz. However, Lilah and Wolfram & Hart Special Operations Team, as well as Angel ambushed Holtz's truck. A tense four-way confrontation between Angel, Wolfram & Hart, Holtz, and Sahjhan ensued beneath a bridge at the edge of town. Since Angel would rather not have Connor in the possession of Wolfram & Hart nor killed, he reluctantly agreed to let Holtz take Connor, and Holtz promised to look after the child as if he was his own son while keeping the identity of his true father a secret.
Sahjhan, who all along hoped Holtz would kill Angel as it could defeat a prophecy claiming Connor would grow up to kill him, threatened to swallow all of them into portal leading to Quor'toth, "the darkest of the dark worlds," but at the last minute Holtz pushed Justine out of the way before he leaped into the hellish portal with Connor clutched in his arms.
For years Connor grew up in Quor'toth, where time moved faster than on Earth. During his childhood and teenage years, Holtz acted as Connor's adoptive father, as well as trainer, teaching the boy to hunt demons and survive, as well as instilling a great hatred for Angel while making him believe Holtz was his true father and giving him the name he intended. Connor eventually found a way to return to Earth which was only months from their arrival to Quor'toth, and an elderly Holtz soon followed.
Back on Earth, Holtz was confronted by Angel and gave him the impression that he no longer wished for revenge and instead wanted Connor to live a healthy life with his biological father. However, this was simply the final phase of his scheme. Reunited with Justine, Holtz asked her to perform one final demonstration of her loyalty: to kill him in order to fulfill his revenge.
Death and legacy
Together, Holtz and Justine simulated a vampire attack by having the latter stab the former in the neck twice with an ice pick, in a manner resembling a vampire's bite. Connor arrived to find his adoptive father's corpse cradled by a saddened Justine. Just as Holtz intended, Connor blamed Angel for Holtz's death and, with Justine's help, abducted Angel, sealed him in a metal coffin, and sank the vampire to the bottom of the sea.
For three months, Connor joined Angel Investigations under the pretext of helping them find Angel, though in reality, he was trying to ensure that they would never find him. However, Wesley kidnapped Justine and forced her to help him find Angel, informing Charles Gunn and Winifred Burkle of Connor's role in Angel's disappearance upon doing so. Upon returning to the Hyperion Hotel, Angel informed Connor of the truth behind Holtz's death and his scheme.
Proceeding these events, Angel and Connor began to develop a more healthy relationship, but Connor's time in Quor'toth, along with Holtz's brutal training regimen and manipulations, had a significant impact on Connor's mental and emotional stability, with the ensuing Jasmine crisis driving him over the edge and causing him to nearly commit suicide. Ultimately, Angel made a deal with Wolfram & Hart to alter reality to give Connor a normal human life and family with no memory of Angel Investigations or Holtz.
However, Connor ultimately regained his memories. With his new human life giving him the emotional support and stability he once lacked, Connor fully reconciled with Angel, rendering Holtz's vengeance moot.