A Monarch geologist and chief cartographer who works closely with Kong and charts the mission into the Hollow Earth. Skarsgård described his character as a reluctant hero who is "not an alpha, bad-ass" and "thrown into this very dangerous situation and is definitely not equipped for it". Skarsgård called Nathan a homage to 80's films like Indiana Jones, Romancing the Stone, Lethal Weapon, and Die Hard.

The daughter of Monarch scientists Mark and the late Emma Russell. Madison believes there is a reason for Godzilla's erratic behavior, suspecting a conspiracy formulated by the Apex Corporation. She proceeds to investigate with Josh Valentine and Bernie Hayes. Brown described the film as a coming of age story for Madison, noting that the character has "grown up" and become more "independent" since the events of the previous film, stating, "Her storyline has definitely evolved greatly in the way she deals with things, her attitude towards life, how much more stronger of a person". Producer Alex Garcia described Madison as the "advocate for Godzilla in this film" who tries to "vindicate" Godzilla and his reasons.

A Monarch anthropological linguist, and Jia's adoptive mother. Hall described her participation as "overwhelming" due to the film being her first project after her pregnancy, but found the experience "thrilling". Hall described Ilene as "the Jane Goodall of Kong".

A former Apex technician turned conspiracy theorist aiding Madison and Josh to expose Apex. Henry described Bernie as a "crackpot" with a level of "heart" and "loyalty". Henry noted that the tragic death of Bernie's wife shaped him to become a conspiracy theorist with a podcast and further elaborated, "his goal is to use the tools at his disposal to bring the truth to the people. I always refer to Bernie as Anonymous. He can see the injustices, but no one really listens to him." Due to Bernie's protective nature of Madison and Josh, Henry jokingly likened Bernie to Brienne of Tarth.