Dyson works in the human world as a homicide police detective in the 39th Division Homicide Squad. Though at first glance he appears middle-aged, he is actually 1,500 years old.
He spent centuries in Ireland serving the Laignach Faelad wolf-shifter King of Ailech with his best friend, Stefan. In terms of shifter tradition, warriors like Dyson fearlessly and unquestioningly believed in total loyalty to their King. This changed when the King betrayed his wolf pack and had his best friend, Stefan, killed to take his wife, Ciara, for himself. After this, Dyson left his pack for good, becoming, in effect, a lone wolf. (This might explain why Dyson sometimes gives the impression of being "cold".)
Dyson is often short tempered and easily aggravated.
He is fearlessly and unquestioningly loyal to his friends and displays a certain respect for rules and the law. However, he shows willingness to bend rules in order to serve his friends, particularly Bo.
He can sometimes be jealous and possessive (especially about Bo).
Like all Wolf-Shifters, Dyson can shift into a wolf. He can also partially shift, changing the nature of his eyes, and his teeth becoming lupine with fangs.
- Bo: The Succubus, and Dyson's relationship first started out as strictly 'sex-for-healing-only', as Dyson made it clear that he didn't want to be in a relationship with her (mostly because Trick told him to avoid it). They eventually became 'Friends with Benefits' and decided to just have heal-sex and fun together without emotions or feelings. Soon, they develop feelings for each other and begin to feel mutual love. When Bo confronted her mother, Aife, in a hand-to-hand battle, he went to The Norn to offer her his "wolf" in exchange for her giving Bo his strength to defeat Aife with. The Norn, instead, tricked him and took away his ability to love Bo or anyone else. However, Kenzi forced The Norn to return Dyson's love by threatening to cut down her sacred tree with a chainsaw in Into the Dark.
- Trick: A Light Fae Elder and bartender/owner of The Dal Riata, the only local Light Fae hangout, Waypoint, and neutral territory for both Light and Dark Fae on La Shoshain. Trick and Dyson have a close relationship that began in 1899 (La Fae Époque), when they first met . Dyson is one of the few people who knows that Trick is The Blood King and will do as the King asks.
- Hale: Another Light Fae detective and a Siren, is Dyson's partner and closest friend, despite some strains on their friendship created by Hale's social status and Dyson having engaged in random sex with Hale's sister, Val. Hale is of Noble blood, but accepts being the "side-kick" to Dyson's "alpha-dog." This dynamic changes, with no apparent problems on either side, when Hale becomes the acting Ash in Season 3.
- Kenzi: Bo's best friend and sidekick, has become Dyson's friend, although she is human and their friendship is also occasionally negatively affected when his relationship with Bo fails; and as such she has stated in Mirror, Mirror that "when Dyson left you it wasn't just your heart he broke." Still, Dyson and Kenzi often support each other in bad situations, including him agreeing not to leave her while she is dying from ingesting a Fae virus in Food for Thought. Kenzi risked her life to retrieve him in Lachlan's Gambit. In Into the Dark, she confronted The Norn and threatened to cut down her Sacred Tree if she did not surrender and return Dyson's love passion. When the Kitsune, Inari, imitated Kenzi's appearance and Dyson thought he had accidentally killed her in The Kenzi Scale, he was clearly devastated at having done so - a situation exacerbated by his doubting his decisions and memories due to an attack by Tamsin. When Lauren confirmed that the body before him was a Fae, not Kenzi, he hugged Lauren for the first time since he'd known her.
- Lauren: The human property of The Ash, who at the start of the series has been in servitude to the Light Fae for five years. Dyson is contemptuous towards humans and as Lauren's status among the Fae is that of property, regardless of being a scientist and physician, he has been dismissive of her, treating her with arrogance and open hostility. When Bo starts to show an interest in Lauren, he becomes jealous and perceives her as a rival. However, he begins to get to know Lauren through Bo, and his negative attitude towards her has gradually diminished, to where he offers her moral support after she breaks up with Bo in Delinquents.
- Ciara: Taught Dyson and his wolf pack the art of war, and he is reunited with her after many centuries in BrotherFae of the Wolves. They start a romantic relationship, but it ends in Midnight Lamp when Dyson tells Ciara that he is unable to love anyone because The Norn took his ability to love after he offered her his wolf. He does, however, tell her that if he could love her, he would.
- The Norn: An ancient and powerful Fae able to grant supplicants their greatest desires in exchange for what they hold dearest. Dyson first sought out The Norn in BrotherFae of the Wolves while he and his pack of Laignach Faelad wolf-shifters served the King of Ailech, after he learned his King intended to have the pack’s leader, Stefan, sent on a suicide mission because he coveted his wife, Ciara. Dyson turned to The Norn to prevent the events from happening. During their meeting The Norn demanded Dyson's "wolf" – his Fae powers – in exchange for saving Stefan. Knowing that his wolf was crucial to his very identity, Dyson could not muster the courage to give it up and thus did not accept The Norn's offer. Stefan died as the manipulative King had hoped for, causing Dyson to renounce his allegiance to him and severing himself from the wolf pack. The second time Dyson called upon The Norn was in Blood Lines, when Bo confronted Aife to stop her war against the Light Fae. At this encounter, Dyson offered The Norn his "wolf" – however, this time the Norn did not accept it as she realized that it was no longer what Dyson held most dear and its loss would not torture him. Instead, she tricked him and took what she knew was now dearest to him: his love. She seized his love for Bo and his ability to love anyone else ever again. The Norn returned Dyson’s love passion after Kenzi threatened to cut down her Sacred Tree if she didn’t (Into the Dark).
- Val Santiago: Hale's sister, displayed more than a passing interest in Dyson and which he began to reciprocate after they had sex, until Hale stepped in between them to end it.
- Chloe (a.k.a. Daphne): Dyson had a brief but intense relationship with the Water Nymph, but failed to return her call.
- "I wish I could tell you there was some grand conspiracy, but there isn't. Vex, Siegfried, Lou Ann...they didn't know anything about your mother. Nobody does." — to Bo (Vexed)
- "Saskia isn't who you think she is. Her real name is Aife and I've been expecting her to come for you for a while now...she is your mother." – to Bo (Blood Lines)
- "You know, it's going to take them a while to select a new Ash. Now might be your best chance...Run. Be free. I know how much that means to you." – to Lauren (Flesh and Blood)
- "Hale told you not to go!...This is why you can't leave the Fae, Lauren. Why you can never leave." — to Lauren (Hail, Hale)
- "I'm ready to pay your price, crone. – to The Norn (You would give up your wolf for this woman? – The Norn) Yes...Reasons are not part of this bargain. If you give my strength to Bo, you can take anything you need." – to The Norn (Blood Lines)
- His romantic relationship with Bo is sometimes referred to as Team Dyson.
- The only time in the series that the surname "Thornwood" has been used for Dyson was in (Dis)Members Only, when he and Bo went undercover as as a married couple at the Queensdale Country Club.
- In La Fae Époque, Bo transports into Dyson's memory of 1899 and she appears as Dyson in the flashbacks.
- In Hail, Hale, Bo smelled the stink of Skunk Ape on the EMTs that put Dyson in their ambulance – the same stink that Lauren used on herself in Caged Fae to fool The Warden, Amazon guards, and Fae prisoners by coating her clothes with the secretions of Skunk Ape so that they would not detect her as human. Bo learned from Lauren that if a Wanblee baby smelled a Skunk Ape it would blow up "like a party balloon." Bo told the EMTs that Dyson was a Wanblee to test if they were actually Skunk Ape Fae and they ignored her, revealing that they were neither.
- Kris Holden-Ried has also appeared as a werewolf in the feature film, Underworld: Awakening. When asked in an interview about playing werewolves in both Underworld: Awakening and in Lost Girl, he pointed out: "Dyson is not so much a 'werewolf' as he is a 'shifter'. He doesn’t lose control of himself at a full moon." 
Dyson (Kris Holden-Ried)
A shape-shifting Light Fae and homicide detective, Dyson is Bo’s mysterious, stoic and handsome love interest. Dyson’s undercover detective work helps protect the Fae while keeping his cover in the human world. A lone wolf at heart, Dyson’s love for Bo has an eternal strength. His allegiance to the Fae and his protective instinct with Bo often gets him into trouble at work. But Dyson, a noble friend and wolf, has no problem risking his life for his friends or for the overall good of the Fae.
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