Daniel Dickinson (Simon Reynolds) was the Deputy Director at Secret Service Headquarters in Washington, D.C. Before Pete and Myka's reassignment to Warehouse 13, he was their boss.
Steven Jinks (Aaron Ashmore) is a former U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) agent who Irene Frederic recruited after having been told by Artie the nature of Warehouse 13.
Though numerous attempts have been made to capture him over the years, he remains large until the Season 2 premiere, "Time Will Tell," when he is killed in the Warehouse.
In his quest to create a virtual artificial intelligence (AI), he attempted to use an artifact to copy his mind into the Warehouse software, which failed.
In Season 2, when the dormant AI emerged and took control of the Warehouse, Artie and the team used the artifact to reverse the process and restore Hugo's mind.
He reappears in the Season 3 episode "Love Sick" to help Artie when an artifact-enhanced computer virus begins to infect people, leading to the cellular degeneration of their bodies and eventually death.
His voice is briefly heard when Artie watches Leena's statement (that all Warehouse employees record upon joining, stating they understand the job's risks), interviewing her.
Theodora Stanton (Paula Boudreau) is a Warehouse Regent who appears in the episodes "Breakdown," "Trials," and "The 40th Floor"; she is also the proprietor of Ted's Restaurant in Univille.
Using the Triangle Shirtwaist Factory fire doorknob, Sally Stukowski (Ashley Williams) tortures and kills her during Walter Sykes' reign of terror.
Lok Archer (name of both character and actor) is a Warehouse Regent who appears briefly in the episodes "Breakdown", "Trials", and "Shadows".
He is the manager of the Valu-Mart in Elk Ridge, South Dakota, which is a cover for the Regent Vault that once safeguarded the Janus Coin containing the essence of Helena G. Wells.
Keeler also has a Master of History degree from the fictional South Dakota University, Rapid City, where he has access to a private Regent Library.
Dr. Abigail Cho (Kelly Hu) is introduced in the Season 4 episode "The Sky's the Limit" as the new proprietress of Leena's Bed and Breakfast.
Dr. Vanessa Calder (Lindsay Wagner) is the official Warehouse physician and, as a cover, works for the Centers for Disease Control and Prevention (CDC).
In college, he conducted experiments with teleportation using Rheticus' Compass, attempting to use it before finding all of the instructions and was believed dead after activating the device.
Claudia and Artie discovered that Joshua had been suspended in inter-dimensional limbo and carried out the final instruction to bring Josh back to the corporeal realm.
Because of this, she visits Pete at Leena's B&B to collect her grandfather's wedding ring, at which point an artifact from Warehouse 2 accidentally falls into her bag.
Todd (Nolan Gerard Funk) was a Univille hardware store clerk who becomes romantically involved with Claudia Donovan in season 2.
An IT guy hired by mobster John Conti to recover a computer hard drive; when he sees some files he shouldn't have, he ends up in South Dakota in the Witness Protection Program.
Fifteen years ago, in a backstory, MacPherson saved her from a burning building using the Phoenix artifact, which drove the final wedge between him and Artie.
Sam Martino (Gabriel Hogan) was a Secret Service Agent previously partnered with Myka Bering and stationed in Denver, Colorado.
In the Season 3 episode "Past Imperfect", Myka, with Pete Latimer's help, solves the mystery of Sam's death and brings justice to those responsible.
Sally Stukowski (Ashley Williams), is an FBI Agent who in actuality is assisting Walter Sykes with his plan to murder the Warehouse Regents.
She is a ruthless and sadistic woman who will torture and kill to achieve her ends, including the brutal murder of Warehouse Regent Theodora Stanton.
Walter Sykes (Anthony Michael Hall) was a young boy bound to his wheelchair who uses Carlo Collodi's Bracelet to give him the ability to control his own body, enabling him to walk.
In "Love Sick", he causes the death of several young women, turning them to clay when a computer virus he creates starts to infect humans after unintentionally interacting with an artifact.
He is recruited by Walter Sykes to hack into Warehouse 13's computer system and steal the Atlas-66 file, which, when decrypted, gives Emily Lake's location and the Janus coin.
He is killed in "Stand" by a guillotine-type device after failing to open the chess lock, which, if solved correctly, unlocks a portal between the ancient Regent sanctum and Warehouse 13.
Brother Adrian (Brent Spiner), a member of the Order of the Black Diamond (a sect under the Vatican's protection), was portrayed by the "evil" within Artie's mind.
In the Season 3 episode "Don't Hate The Player", it is revealed that he tried to create a virtual reality neural interface video game called the B.R.A.I.D and based on Warehouse 13, using a dangerous artifact, Beatrix Potter's tea set.