Zaggar

Zaggar is the het ship between Emperor Zarkon and Haggar from the Voltron: Legendary Defender fandom.

Canon
Over 10,000 years ago, before the events of the series, a trans-reality comet crashed into Zarkon's home planet, Daibazaal. His allies from planet Altea came to investigate, including an Altean alchemist named Honerva. As Honerva studied the rift left by the comet, Zarkon fell in love with her and married her. Honerva and Zarkon soon became obsessed with quintessence, unfathomable energy found inside the rift, at the expense of the planet's stability and Honerva's health.

Zarkon tricked his allies into using Voltron to expand the rift, making them believe it must be done first in order to close it; he exited Voltron and entered the rift with the deathly ill Honerva, attempting to heal her with quintessence, but both were overcome by dark creatures from another reality. The ordeal left them both presumably dead and a funeral was held. However, Zarkon suddenly reawakened, changed and corrupted into an evil being, as did Honerva.

Honerva seemingly forgot her previous life and became known as Haggar, a witch serving as the high priestess of a group of Druids that support Zarkon's evil Galra Empire. It is not known if Zarkon is aware that Haggar is his former wife. Haggar does not regain her memories until prying into the mind of Zarkon when he is comatose, in an attempt to revive him.

Fanon
Fans suspected that there was something between Zarkon and Haggar at the end of season 2, when Haggar seemed more worried about Zarkon's self-destructive habits than anyone else. When the couple was confirmed canon, fans then went on to try and draw parallels between Zaggar and their own favorite ships, mostly Sheith.

Children
Prince Lotor Lotor was conceived 10,000 years ago, before Honerva entered the rift; he has stated that Honerva is his mother and that Zarkon is his father. While he is aware that Haggar used to be Honerva, he believes that the one he could call his mother died all those years ago. He is disdainful of both Zarkon and Haggar, but has seemed proud of Honerva's experiments on Daibazaal's trans-reality rift.

Fandom
AO3

Trivia

 * From the canon material, some fans notice similarities of the ship to Sheith, due to Keith and Shiro's strong connection to each other.