Clint Howard (Creepy Orion) previously played Balok in The Corbomite Maneuver (1966), Grady in Past Tense, Part II (1995) and Muk in Acquisition (2002). Howard is the first actor to appear in both Star Trek (1966) and Star Trek: Discovery (2017). He has the distinction of being the actor whose appearances span the longest time interval (51 years) in the history of the "Star Trek" franchise.
A Trill woman can be seen receiving a tattoo on Qonos. This marks the earliest canonical appearance of a Trill.
In the mirror universe, Emperor Georgiou and Captain Tilly wiped out Mintaka III. The U.S.S. Enterprise (NCC-1701-D) visited this planet in 2366 in the primary universe in Who Watches the Watchers (1989).
This episode marks the first appearance of the U.S.S. Enterprise (NCC-1701) in Star Trek: Discovery (2017). Disregarding the brief appearance of the ship in the epilogue of These Are the Voyages... (2005), this is the first time that the Prime version of the U.S.S. Enterprise (NCC-1701) has been shown on screen since Trials and Tribble-ations (1996). This does not include appearances in the Kelvin timeline, as depicted in Star Trek (2009), Star Trek: Into Darkness (2013), and Star Trek: Beyond (2016).
A slightly updated version of the Star Trek (1966) theme was played over the closing credits instead of the usual Star Trek: Discovery (2017) closing theme.