Doctor Dio Zardeliv (or possibly Zardilev) was a at a university in Paris (probably the Paris Institute of the Extraordinary) with an obsession with clocks and time. He is the author of a six-volume treatise on Potential Widdershins Chronoparticle Spin, which was required reading in one of Agatha's classes with Doctor Beetle. He is the great-uncle of Violetta, who grew up knowing him as  According to her, he has no interest in their family's endless internal power-struggles.
After Mechanicsburg is sealed off in a time stasis, his lectures on the mechanics of time become incredibly popular within the school, and he becomes a celebrity in greater Paris society. This in turn leads to the first of several attempts on his life (there are many powerful individuals who do not want Mechanicsburg freed) and to his retreating into the extensive world of the Parisian Black Market, in search of a notebook that "one of his idiot nephews lost". Despite an important missing key, his office is taken over and his clocks wound by his fellow professor Drusus Beausoleil, while his more promising students all go to assist in Gil's ongoing efforts to unseal Mechanicsburg. When Agatha arrives in Paris a year and a half later, Zardilev is still officially among the missing, though she eventually learns that he went to ground specifically in The Incorruptible Republic of the Immortal Library of the Grand Architect. However, the assassins follow him even there, leading him to go further into hiding, inside the Library's sealed-off ex-Corbettite artifact vaults; the notebook details the extensive trap network the Monks installed. Along with avoiding death (by assassin at least), it is possible that Zardilev is also seeking a semi-mythical time-manipulating object known as Prende's Chronometric Lantern.
In the Comic
When he finally appears Smoke Knight and Lucrezia-follower Madwa Korel as they struggle to break into a particularly secure vault. Following the arrival of Agatha and her exploration party, he gets gassed into unconsciousness and it is revealed the vault does indeed contain a time-altering lantern; Madwa spirits away both this device and Zardilev. Their ultimate destination is England via submarine. Agatha and Co. get there ahead of them, and meet the sub when it comes crashing into the docks. It is revealed that everyone on board is dead via poison gas; Violetta explicitly Zardeliv as one of the victims, while the body assumed to be Korel is notably kept off-camera. There is no sign of the Lantern., he is shown working with the
How Do You Spell That?
This character's last name has been spelled as both Zardeliv and Zardilev in the comic. The last several times he has been mentioned, however, the spelling Zardeliv has been used and seems likely to be the one the Foglios intended.
Technical note: How to refer to this character in the wiki
Given that this character is usually referred to as Professor (or Doctor) Zardeliv, rather than by his first name, and the frequency with which the variant spelling Zardilev is used, two redirects have been created for "Zardeliv" and "Zardilev", both going to this page. This will allow you, in a Chronology entry for a page mentioning the name of this character, to use the spelling from that page and link by last name only, using the title given on the page. For example, Professor Zardeliv or Doctor Zardilev. In the source editor, it would look like this:
Both links would redirect to this page. If the name is spelled multiple ways on a page, this should be noted. If the Foglios revised the comic to use a consistent spelling in the future, then the wiki should eventually be updated.
Possibly Relevant Outside Information
"Dio" is the Italian word for God, but it is quite possible that the Doctor is a reference to another character with the name of Dio and time control powers: Dio Brando the vampiric antagonist of the first and third arcs of the Japanese Manga JoJo's Bizarre Adventure. Zard is persian/hindu for yellow (anemic?) and liv is life in several languages.