Kingdom

Ta Hab (special), Ashin's father and head of the Northern Seongjeoyain tribe.

Won Yu (season 2), descendant of an exiled member of the royal family living a quiet life on remote island, who is sought out by Lee Chang.

Eunuch (season 2), a former eunuch who later becomes the new king's servant.

Seo-bi, a physician from Dongnae, and one of the only two survivors of the plague's original outbreak. She desperately seeks to find a cure, and comes to possess a journal containing crucial information about the disease.

Cho Beom-il (seasons 1–2; special), Cho-Hak-ju's son and Queen Cho's elder brother and a commander in the Royal Army.

King Yi Yeom (season 2), Mu-yeong's son who was rescued from a horde of zombies as a baby by Seo-bi.

Mu-yeong's wife, who is pregnant and was put under the protection of the Haewon Cho clan.

Cho Beom-pal, a magistrate of Dongnae and Cho Hak-ju's nephew, shown to have somewhat of a good nature but to be incompetent and easily scared.

Yeong-shin, a mysterious tiger hunter from the South who is the only survivor of the first outbreak. A strong fighter uniquely skilled with novel matchlock muskets and who shares little of his past, he allies himself with Lee Chang and helps to lead the fight against the undead.

Lee Gang-yun (season 2), head of the Royal Army, who travels south with Cho Hak-ju.

Young Ashin (special)

Lee Chang, the Crown Prince of Joseon and heir presumptive to the throne. Although he is the King's only child, his late mother was unmarried, meaning that a son born from the Queen Consort would become the heir apparent and new Crown Prince. Suspicious of the illness afflicting the King, and his recent lack of public appearances, his investigation not only uncovers a dangerous plague that brings the dead back to life, but also a plot to betray the Royal family and usurp him as heir.

Lord Cho Hak-ju (seasons 1–2), the Chief State Councilor of Joseon who is the head of the Haewon Cho clan and Lee Chang's political rival. He is the father of Queen Consort Cho and Cho Beom-il, and the uncle of Cho Beom-pal. A cold, ruthless leader, he is desperate to secure his power over the throne through Queen Cho's unborn child who he seeks to make heir to the throne in place of Lee Chang.

Queen Consort Cho (seasons 1–2), the young and pregnant Queen of Joseon, and the King's wife. She is Cho Hak-ju's daughter, Cho Beom-il's sister and Lee Chang's stepmother. Like her father, she is desperate to secure her power over the throne by giving birth to a son that will displace Crown Prince Lee Chang as the rightful heir.

Mu-yeong (seasons 1–2), Prince Chang's loyal personal bodyguard who accompanies him to the southern provinces to investigate the plague, leaving his pregnant wife in the capital.

Lord Ahn Hyeon (regular season 1; recurring season 2), a former governor considered a war hero for his part in the Imjin War. Despite his popularity with the people, he retired from public service to live a quiet life in Sangju. He was also a mentor to the young Lee Chang.

Ashin (guest season 2; main in special), a mysterious woman from the Hamgyong Province in the North of the country. Kim Si-a as young Ashin (special)