A strangely detached fellow (an odd characteristic for a Hawk) with an almost endless supply of curiosity, combined with an Asperger's-like immunity to social cues. He seems to be deeply well-informed about psychic powers, and curious to learn any aspects he hasn't mastered.
Vlad finds him irritating, for reasons which, even if Vlad could articulate them, would undoubtedly bewilder Daymar.
Daymar is good friends with Kragar, who met him some years ago. He continues to help Vlad whenever asked, despite Vlad's continual irritation, and despite rarely receiving favors or compensation in return. This may indicate that Daymar considers himself friends with Vlad as well, or perhaps he's just grateful for the continual new information and experience (and chances to show off) that he gets from helping Vlad out.
Loiosh knows where Daymar lives, but has evidently never passed that information on to Vlad. Vlad does know that Daymar is associated with Pamlar University.
We know nothing about Daymar's early life. At least one of his parents is presumably deceased, as Hawk reveals that Daymar inherited an enchanted wand from an eccentric uncle, who had no other living relatives.
Daymar first met Vlad during the events of Dragon. Vlad entered a room filled with Morganti weapons, and found the combined effect of their many predatory auras to be overwhelming. In addition, he needed a way to somehow detect the (expected) theft of any of the weapons. Kragar thought that Daymar's psychic ability might be able to help in some way.
After being introduced to Vlad, Daymar was indeed able to reduce the effect of the Morganti auras on Vlad. However, Daymar then made several faux pas, the worst of which was to mind probe Kragar about what Vlad was trying to do and why. Vlad threatened Daymar with a Morganti dagger from the collection, telling him never to do anything like that again.
Daymar then offered to put a psychic trace on the room such that the theft of one or more swords would register with Daymar.
Vlad went and agreed with this, and the next day, Daymar contacted Kragar with the information that one of the swords had indeed been stolen.
While Vlad had a bad reaction to Daymar's social ineptitude, he later realized that Daymar's psychic powers could be of enormous use during the Battle of Baritt's Tomb. Daymar managed to overcome the teleport block on the battlefield, and agreed to help Vlad by mind-probing Fornia, and transmit the information to Vlad, who then managed to thwart Fornia's plan.
Later, when Vlad was faced with a difficult piece of work, killing a former Jhereg Council member named Mellar, Daymar was crucial in resolving the situation by assisting with an elaborate illusion which allowed Vlad to take the place of one of Mellar's bodyguards. He also performed a mindscan of Mellar at a critical moment, leading to the recovery of millions of Imperials for the Council.
Daymar later participated in the effort to rescue Vlad from Greenaere, after Vlad has assassinated the king Haro Olithorvold. He also aided Vlad in returning to the island after war had broken out, in order to broker a peace agreement.
Assisting Vlad in the investigation of the activities of the Left Hand of the Jhereg several years afterward, Daymar tried (fairly unsuccessfully) to explain to Vlad the workings of Psychic energy fields, and also to learn some information about Crithnak, a sorceress with whom Vlad had come into conflict.
More recently, Daymar assisted Vlad's investigation into the politically motivated arrest of Aliera e'Kieron. Unsurprisingly for Vlad's only Hawklord friend, Daymar plays a major part in the events of Hawk.
As detailed in the Steven Brust’s short story, The Desecrator, sometime prior to the Vlad storyline, Daymar worked as a desecrator (a Dragaeran archeologist) for Pamlar University. He was is the process of desecrating an abandoned Serioli dwelling where he met Telnan who was sent by Sethra Lavode to investigate an amorphic anomaly caused by Nightslayer. Daymar’s psychic probing awoke Nightslayer, who didn’t care for him much. After putting Telnan in psychic contact with Nightslayer, Daymar wisely ran away.
Oh, that was irony, wasn't it?
Napper, observing Daymar's lack of a blade: He's not armed.
Daymar, sounding slightly offended: I most certainly am.