Vesper One is the leader of the Vespers, and the Vesper with the highest authority in the The Vesper Council of Six. His job is to give directions to the other Vespers and to execute all plans. The most recent Vesper One is Damien Vesper III, a descendant of the original Damien Vesper.
He delivers a super secure phone to Amy and Dan via helicopter and gives them their assignment: If they don't follow his instructions, one of the hostages will die. They are forced to steal the Medusa. He has been leaving them messages throughout the book about their assignments. He hires an acrobat in a circus to take the Medusa from Amy and Dan. He murders the acrobat, who reveals on her last breath that he has a burn on his arm. At the very end of the book, it is revealed that the taxi driver who had driven Amy and Dan around since the Colosseum was actually Vesper one.
Vesper One asked Amy and Dan to steal the de Virga Mappa Mundi. He took the de Virga and the Il Milione. He then sent a text to Amy and Dan saying that they should have told him that they had the Il Milione, and their consequences are this: one Guardian goes down: Dan's best friend, Atticus.
Vesper One will be asking them to find a stale orb which is an anagram for an astrolabe, a device to measure the stars. He is supposedly at the drop off again, and is seen blowing kisses (in mockery) at them.
He forced Amy and Dan to try to steal the Jubilee diamond from the Museum. He meets up with the escaped hostages and told them he was Martin Holds, then he faked his death.
He visits Atticus, Jake, Amy and Dan at the building where the Voynich rested. He offers to buy them meals. Later, he is mentioned when Ted told Nellie that he recognized Martin Holds' voice as Riley McGrath's (though it was unknown to Ted that Riley and Martin were the same person). He later sent a dog ("Goldilocks") to take Folio 74 of the Voynich and Gideon's ring to complete the Machina Fini Mundi.
He addresses Amy and Dan through a video and informs them that all the hostages are not going to be freed. He then rides a plane in turbulent weather and heads off to the Cascades. Then, through his super secure phone, instructs his men to kill Isabel Kabra. He then promotes Sandy Bancroft to Vesper Two. He shoots Fiske in the shoulder and Evan fatally in the chest. He turns on the electromagnetic shield of the Machina Fini Mundi and electrocutes Natalie, but gets shoved into Machina Fini Mundi by Isabel Kabra and gets melted into the machine and gets incinerated along with her.
The suspects were:
- Damien Vesper III (a.k.a Dave Speminer) - who was Astrid Rosenbloom's assistant before her death. It is possible that he may have killed her. Dave Speminer's name is also an anagram of Damien Vesper. He also has a burn on his arm and hand, if you look closely at Card 312: Dave Speminer. Dave turned out to just be an alias of his.
- Damien Vesper I- as a code in The Medusa Plot says "Damien is Alive" and he has a burn on his arm, possibly inflicted by the Great Cahill Fire. "Damien is Alive" is possibly an anagram. Damien was most likely to be Vesper One because he founded the Vespers. Although he ended up to just be a descendant of the original Damien Vesper, as they all share the same name.
- Arthur Trent - he was raised among the Vespers, was thought to have escaped the fire that killed him and his wife, and there are many hints in the books contributing to this theory. Until, Dan discovered that Isabel Kabra was texting all those messages under AJT using a back-up cell phone.
- Vesper One's identity is only known to the people in the Council of Six. Except Casper Wyoming, as he was banned from the Council of Six.
- He has a healed burn on his arm which occasionally itches, although it is revealed that the urge to scratch it was merely psychological, especially when other Vespers failed him. And he considers it to be a "badge of honor", probably since his ancestor, Damien Vesper I, had one as well.
- He has directly walked up to Amy and Dan Cahill in "The Medusa Plot" and "Trust No One" and did not harm them.
- He is afraid of boats and open water.
- His New Year`s resolution was "World Domination".
- Damien Vesper II was probably Vesper One before Damien Vesper III. He died in 2007.
- In The Medusa Plot there is a fingerprint on the last page probably his.
- In Trust No One it is revealed that he has a taste for luxury, by always having his meetings in exotic cities like London, Paris etc.
- Damien Vesper II had met Arthur Trent and seen him as an potential Vesper.
- In 2013, he infiltrated the Message Board as a Rookie Agent Tomas.
- He is originally from Ireland.
- He is blue-blooded, as his ancestor, Damien Vesper I, was a Lord in the 1500's. That is revealed in the Gideon Cahill section of Vespers Risng.