This page is not intended as a complete synopsis of Greg Herd's character, rather, an overview of the events that took place following the Gathering of Five ritual.
Dr. Greg Herd was first introduced during the Clone Saga alongside his wife Ann, as the cybernetically enhanced duo known as Override and Aura. As Override, Herd had the capability of "overriding" any mechanical device, while Aura has the capability of projecting force fields. The two worked as mercenaries, utilizing their powers for the highest bidder.
Ann was nearly killed in Sensational Spider-Man #25 when a "slazer beam" was trapped inside a force field she had projected while they were trying to capture Spider-Man during the Spider-Hunt Saga. She soon fell into a coma as she was placed in intensive care in order to treat her numerous injuries. This incident greatly affected Greg, since he did not have the financial resources (nor the insurance apparently) to pay for her medical expenses. The need for cash forced Herd to fall in with Norman Osborn and the temptation of the Gathering of Five ritual was too much for Herd to resist. Herd was thus unique amongst the other participants in the Gathering, since his motivations were less selfish and aimed at restoring his wife's health.
In Amazing Spider-Man #441, as the gifts were being "distributed" it appeared as though Greg had recieved the gift of immortality. But that was not the case, Madame Web recieved immortality and instead Herd recieved a unique form of death. This "death" that he recieved causes his body to be engulfed in flames from the inside out, leading to what is an inevitable and excruciatingly slow death.
Herd resurfaces in Amazing Spider-Man V2 #2, where, as Shadrac, he attempts to break into an Osborn Industries safe to retrieve the spindle from the Gathering. Mattie Franklin, who is disguised as Spider-Man, tries to stop Shadrac but fails. Luckily, Peter was nearby and was able to save Mattie from Shadrac, however the villain did manage to escape.
The shroud of mystery surrounding Shadrac/Herd was partially uncovered in Amazing Spider-Man V2 #3, which introduces the villain known as Dolman. Dolman claims to have had the spindle in his possession for a very long period of time until it was stolen from him by Norman Osborn (specifically "agents of Osborn"). The spindle had bestowed powers to Dolman, even though he had never participated in a Gathering of Five ritual with it. Dolman claims to have a bond with the spindle, which allows him to track the shard, and this bond also allows him to sieze control of Herd's mind as Shadrac. Interestingly, when the actual Gathering of Five ritual was performed, the power surge caused Dolman to be placed in the hospital for weeks.
The battle between Dolman and Shadrac continues in Peter Parker Spider-Man V2 #3 as Spidey and Iceman track the duo down to a subterranean chasm beneath New York City. Dolman seeks possession of the central piece once again because he claims that that will give him control over all the other members of the Gathering and their respective powers. Dolman also claims to have given Herd his new name Shadrac. When it became apparent that Dolman was too powerful for Spider-Man, Iceman, and Shadrac to stop, Herd decided to use his powers as Override to neutralize Dolman. This tactic works, however, Dolman and Herd become merged as one being at the conclusion of the story, with Herd being able "override" whatever evil Dolman attempts.
Dolman re-enters the Spiderverse once again in Spider-Woman V3 #3 as he employs the villainess Flesh and Bones to hunt down the lost shards. She is also unsuccessful at doing so. In Spider-Woman V3 #4, Dolman explains that his fusion with Herd was only partially complete and he is now calling himself Shadraq (not really sure how anyone listening to him say that could recognize that he even changed anything). He explains to Spider-Woman III that he was "born of power beyond the measure of space and time" and that at one point all of the shards necessary for the Gathering were in his possession. But he lost track of them over hundreds of years. In a very anti-climatic ending, Dolman gives up on his efforts to find the shards, claiming that all his plans are now ruined. He then disintegrates into a pile of ash and smoke.
Dr. Greg Herd's escape from his fusion with Dolman and his current location (along with that of his wife Ann's) are currently unknown.
Greg Herd alongside his wife Ann as she lays unconscious, as seen in Sensational Spider-Man #33
Dolman confronts Shadrac and reveals his plan to him, as seen in Amazing Spider-Man V2 #3
Shadrac and Dolman merge into one being as Shadrac uses his "override" capabilities to thwart the villain, as seen in Peter Parker Spider-Man V2 #3