While Xanatos was still in prison in late 1994, he arranged for a Steel Clan robot to attack Goliath and wound him, afterwards having Owen obtain some cell samples from the gargoyle under the guise of treating his injuries. Sevarius used the genetic material to create Thailog, artificially aging him to the same biological age as Goliath in a matter of months; he also tutored him through subliminal methods, indoctrinating him in Xanatos' ethical code of utter amoral pragmatism.  Thus Thailog was "born" in 1995 with a fully grown gargoyle body and a keen, advanced, if twisted, mind.
Xanatos and Sevarius succeeded too well in their goal of creating a replacement for Goliath and his clan; Thailog decided to go into business for himself, and duped Sevarius into "kidnapping" him and holding him for a twenty million dollar ransom. When Xanatos came to pay the ransom, Thailog ambushed both him and Sevarius, seized the money for himself, and planned to kill them both by locking them up within an abandoned oil rig off Black Rock Point and setting the barrels of oil there on fire.
Aware of his origins, he arranged (with a bit of an effort on his part) for his third "father", Goliath, to join him there, originally considering to share the money with him. But when Goliath initially regarded him as an abomination and made that clear in no uncertain terms, Thailog decided to kill him as well. Elisa rescued all three of Thailog's "fathers" from death, but Thailog escaped with the money. ("Double Jeopardy")
He went to Paris, where, not long afterwards, he met Demona. Deciding to make use of her for his own ends (and probably physically attracted to her in the bargain), he became her mate, and they decided to pool their resources, forming Nightstone Unlimited. They also decided to add to their wealth through Demona wedding Macbeth as Dominique Destine, then afterwards locking him up and making him appear to be dead so that she could inherit his wealth; Thailog, however, plotted to turn this to his own advantage again by tricking Demona and Macbeth into killing each other so that he could inherit all their wealth. Elisa managed to foil this scheme when she and her companions arrived in Paris during the Avalon World Tour, but Thailog and Demona fled Paris together, Demona still none the wiser about her mate’s betrayal of her. ("Sanctuary")
They later on returned to New York, where they arranged for Demona to be captured by the clan so that she could first arrange to have the gargoyles cloned using robotic mosquitoes, supplying herself and Thailog with followers, and then escape, leading Goliath's clan into a trap. Thailog directed Sevarius in the creating of the clones of Hudson and the Trio, but had him secretly create a fifth being from the DNA of Demona and Elisa, Delilah, whom Thailog intended for his new mate (he had already decided to dispose of Demona, whom he considered too much of a loose cannon).
The scheme proceeded according to plan, until Thailog, having captured the clan, ordered Angela's death; Demona protested this, and after learning about Delilah, furiously turned on him. The two wound up fighting each other in the middle of a burning roller coaster at Coney Island, where Thailog appeared to perish. ("The Reckoning") In actuality, Thailog managed to pull himself free as the roller coaster collapsed and glided away amid the chaos. Labyrinth. ("Invitation Only") After regaining control of the clones, he took them to the Eyrie Building under the pretense of coming to reclaim Delilah. He was confronted by Goliath and Owen Burnett, the latter confiscated Thailog's weapons in exchange for bringing him Delilah. But, treacherous as ever, Thailog stabbed Goliath in his abdomen with a hidden blade in his gauntlet. ("Masque") Thailog then proceeded to torture Goliath before Elisa and the rest of the gargoyles arrived, whereupon Thailog made sure to slash each and every one of them with a series of pristine blades in his rotating gauntlets. The battle ceased when Delilah arrived, stating she had no intention of siding with Goliath or Thailog. Most of the clones returned to the Labyrinth with her, except for Brentwood, who chose to return to Nightstone Unlimited with Thailog.
Thailog met Sevarius and revealed that his plan was a complete success, and that his real objective was to collect DNA samples from all the gargoyles as well as Elisa (which is why each opponent was struck with a clean blade which was thereafter retracted for storage). The defection of Brentwood and the severe wounding of Goliath were simply incidental additional achievements in the mission. At that moment, Shari appeared, offering to become Thailog's new executive assistant. At first, Thailog appeared ready to kill her, but upon spotting an Illuminati pendant on her, he dismissed Sevarius and Brentwood, and greeted Shari as a member of the Illuminati, which he had recently joined as a lower echelon member. ("Bash") He then took Shari into his service.
For several nights, Thailog listened intently as Shari told him stories about the history of the Stone of Destiny. ("The Rock", ""Rock & Roll", "Rock of Ages") He was also brought in by Falstaff to speak to Yama and Fang over a videoscreen in an effort to recruit the Redemption Squad into the Illuminati (though at first Yama mistook him for Goliath and thought the color on the screen needed fixing). Ironically, Thailog's presence in the Society, along with Fang "vouching" for him, caused the Redemption Squad to turn down the offer. ("Losers")
Thailog will still be alive and will make an unspecified attack in 2009. 
Physically, Thailog bears a striking resemblance to Goliath, although with altered coloring because of his artificially-accelerated aging. As a result, his hair is white, his eyes are red, his skin is a dark purple/indigo shade, and his wing membranes are pale lilac. He often wears battle armor and a helmet, which he obtained after his escape from Black Rock Point, though at times he has been seen without the armor or in other clothing such as a Roman toga.
Thailog is one of the most thoroughly malevolent of the Manhattan Clan's adversaries. Thoroughly cunning and duplicitous, he will happily betray anybody for his own benefit, and is ever ready to enrich himself at others' expense. He also seems to have something of an Oedipus complex, both in his attempts to kill his "fathers", especially Goliath, and in his choice for mates (first Demona, who was Goliath's past mate, and then Delilah, a genetic amalgamation of Demona and Elisa). He is an archetypal bastard, and rivals Xanatos in his wiliness as a trickster.
After his escape from the oil rig at Black Rock Point with Xanatos' money, Thailog adopted the human alias of Alexander Thailog, a reclusive financier whom nobody has ever seen. In this guise he co-founded Nightstone Unlimited with Demona, and he now presumably uses this name in his current position as Nightstone's CEO. He chose the name "Alexander" as an homage to Alexander the Great, the famous Macedonian king who conquered a great portion of the known world in the 4th century B.C., as an echo of his own ambitions. 
Thailog runs Nightstone Unlimited by speaker-phone, memo, and e-mail to keep his employees from learning his true nature. 
Thailog also seems to have a fondness for stories, as he has had Shari tell him several since taking her into his service.
- "Double Jeopardy" (First Appearance)
- "Future Tense" (Mentioned Only)
- "The Reckoning"
- "Invitation Only"
- "The Rock" (No Lines)
- "Rock & Roll"
- "Rock of Ages"
Voice Actor: Keith David
Thailog was created out of a desire to further explore Keith David's voice acting abilities (specifically in playing a villainous character), but also from hearing audio tapes being rewound during production of Gargoyles. "Thailog" is a phonetic reversal of the word "Goliath", and every time Goliath's name was read backwards it sounded like the word "Thailog" repeated many times.
In creating Thailog (and, later, the other clones), Greg Weisman wanted to avoid creating an identical evil twin that could take the place of the hero and confuse everyone (since he felt this idea "had been done to death"). The altered skin pigmentation (caused, in-universe, by the clone's artificially accelerated aging) was a way of avoiding this. The specifics of Thailog's look were "partially inspired by the changes that John Byrne made to the Fantastic Four's costumes in the eighties", specifically on their return from the Negative Zone. (Greg Weisman has also said that Negaduck, a villain from the Disney series Darkwing Duck, may also have been an inspiration.) 
Greg Weisman first figured Thailog was a member of the Illuminati after the series already ended, in 1999. 
In 2000, Greg Weisman wrote the Buzz Lightyear of Star Command episode, "Clone Rangers". The episode featured a scene parodying Thailog's name with Buzz's clone, Zzub.