Polaris (Lorna Dane), Magneto's daughter, makes her live-action debut in this feature. She is the third of Magneto's children to appear in the X-Men films universe, after her half-brother Quicksilver (Peter Maximoff) in X-Men: Days of Future Past (2014) and her half-sister in Apocalypse. Though Quicksilver was also featured in the Marvel Cinematic Universe, alongside his twin sister, Scarlet Witch (Wanda Maximoff) in Avengers: Age of Ultron (2015), it's unlikely we'll see their half-sister Polaris in the MCU because the film rights to that character belong to 20th Century Fox.
A main character in this series, John Proudstar/Thunderbird died shortly after his first appearance in "Giant-Size X-Men" #1 in 1975. His legacy continued with his younger brother X-Men James Proudstar/Warpath whom John more strongly resembles on the show.
Towards the end of Season 1, Episode 12, when the mutant way station is shown you can see a sign on a fence that says "J. Kirby's", a reference to Jack Kirby, one of the creators of X-men for marvel comics.
Elena Satine's third portrayal of a comic book character after starring as DC's Mera on Smallville (2001) and Marvel's Lorelei on Agents of S.H.I.E.L.D. (2013). She was also considered for the role of Mary Jane Watson in the infamous musical "Spider-Man: Turn Off the Dark".
As indicated in another post, each episode title has a specific letter capitalized (for season 1 it's the "X" and for season 2 it's the "M"). Given the film series this show is connected to, if the title naming "standard" continues with choosing a seemingly random letter in each title of a season, by season 4 the letters capitalized should spell out "XMEN".
There are several references to X-Men: First Class (2011). The Stepford Cuckoos, The triplets of Emma Frost play a major role in the second half of the season. The Hellfire Club makes an appearance in the series. Polaris' father was described as a "king" in the Hellfire Club. This is a reference to Magneto taking over the Hellfire Club and later turning it into the Brotherhood of Mutants.
In the comics, the Stepford Cuckoo's names spelled out SPICE (Sophie, Phoebe, Irma, Celeste and Esme) as in "what girls are made off" - a subtle reference to their artificial creation. The three living sisters' names in the series spell ESP (Esme, Sophie and Phoebe). ESP is the ability of extrasensory perception, a possible reference to the sisters vast telepathic powers.
The live action debut of the Stepford Cuckoos. In the comics they are artificially created clones of Emma Frost, who have vast telepathic powers and can combine to become even stronger. They were are originally five sisters - Sophie, Phoebe, Irma, Celeste and Esme (SPICE). Esme and Sophie died in the comics, while Celeste and Irma are deceased in the series.