The Two Stargate Atlantis Actors You Didn't Know Were Siblings In Real-Life

This post contains spoilers for "Stargate Atlantis."

Doctor Rodney McKay (David Hewlett) is integral to the "Stargate" franchise. A scientist who joins the Stargate Program in "Stargate SG-1," McKay plays a more prominent role in all five seasons of "Stargate Atlantis," which follows a brand new exploratory mission encircling the eponymous lost city. In case you need a quick refresher on McKay, I got you: He was stationed at Area 51 before his involvement with Stargate Command and helped out the SG-1 crew at several points with his brilliant scientific expertise. After Atlantis was discovered in the Pegasus Galaxy (along with the terrifying regime of the Wraiths), McKay was assigned to the mission, during which he amassed extensive knowledge on the Ancients as the crew's chief scientific advisor.

A certain season 3 episode of "Stargate Atlantis" gives us more insight into McKay's life outside his professional relationships. Titled "McKay and Mrs. Miller," the episode introduces us to his sister, Jeannie Miller (Kate Hewlett), who is also a gifted scientist trying to come up with a solution for the zero point energy problem (a mathematical theory that can bridge two realities). After she submits her formula to scientific peers, she is approached by the Stargate Command soon after, but Miller perceives their offer as an exploitation of her theoretical work. The only person who has a chance to convince her is her brother, so a bickering McKay and Miller talk it out until she finds herself aboard the expedition spacecraft, The Daedalus.

It is no coincidence that the actors who play McKay and Miller share the same surname, as David and Kate Hewlett happen to be siblings in real life. This is truly incredible casting, making McKay and Miller's familial dynamic on the show feel more authentic, especially when they argue irritably over their mutual grievances. How did this perfect casting come about?

In the season 1 episode "Hot Zone," the story takes a dark turn when scientists from the Atlantis expedition start to hallucinate and drop dead after a post-storm damage survey of the planet. McKay deduces that he might be next, but keeps trying to dissect the sudden crisis, which turns out to be the work of Nanites (microscopic machines that can enter bodies, just like organic microorganisms). During this critical juncture, McKay mentions his sister, even though she isn't explicitly named in the episode. Turns out, the script for this episode initially intended McKay to have a brother back on Earth, but David Hewlett requested a change on the off chance that the producers would cast his sister Kate down the line.

According to GateWorld, "Stargate Atlantis" screenwriter and co-producer Martin Gero agreed, and Kate was eventually called in to audition for Miller after Gero saw her perform in a play. "Boy, she's got a lot of Hewlett-isms!" is how Gero apparently reacted to her performance on stage. Well, at least this is how David Hewlett recounted the story, explaining that a brother-sister dynamic seemed like it would be more fun to explore in the event that the "Atlantis" writers decided to flesh out the show's core crew beyond their contributions to the mission. Thankfully, the show eventually did just that, providing us with a sibling dynamic that perfectly illustrates the simultaneous synergy and conflict that comes with working closely alongside family.

Kate and David Hewlett's Gateworld interview also revealed that the latter wasn't supposed to return in "Stargate Atlantis" as McKay but as a brand new character named Dr. Benjamin Ingram. "There's no way that you can play McKay and then show up as a different character a year later," David Hewlett explained. This logic prevailed, leading to a complete rewrite of the Ingram character into the McKay "Stargate" fans know and love. The show is better for it, too, as the return of a familiar face helped solidify a link between "SG-1" and "Atlantis," even though they focus on completely disparate aspects of the larger "Stargate" universe.