The Princess of Planet Arus, her kingdom was nearly destroyed by the forces of Planet Doom when she was a baby, and then she was raised in hiding. When five space explorers (Keith, Sven, Pidge, Lance and Hunk) reach her ruined castle she explains to them the legend of Voltron and helps them find the keys to the lions. Once Voltron is formed, Planet Dooms forces weaken on Planet Arus, which allows the people to rebuild.
When one of the explorers (Sven) is injured by the witch Haggar, Allura takes it upon herself to ride the Blue Lion. Once Prince Lotor arrives to try and take over Arus, he notices how beatiful Allura is and at first tries to make her a concubine. When that fails and he sees the power of Voltron, he decides to make Allura his bride so he can take over Arus directly. However, Allura is repulsed by his obsession and repeatedly rebuffs his advances. Each time she escapes him and rejects him, the more Allura fascinates him and becomes obsessed with marrying her. His feelings for her became so strong he can't even destroy a hologram of her, and he captures her beautiful cousin Princess Romelle because she looks like Allura. His obsession with her is also his greatest weakness, because if he didn't have it, he would have been abe to destroy Voltron.
Lotor's obsession with her carries onto Voltron: the Third Dimension, one episode of Voltron Force; but in Voltron: Legendary Defender, it's shown as less of an obsession and more as a genuine desire for kinship, though mixed with his other ambitions.
In the original Beast King Go-Lion, Allura is known as Fala and Lotor is known as Sincline. In Beast King GoLion, Sincline's obsession with Fala is because Fala resembles his dead mother.
Despite being an English dub, Voltron created its own franchise separate from Beast King GoLion. Voltron has created two spin-off shows, Voltron: the Third Dimension and Voltron Force, and an Alternate Universe one known as Voltron: Legendary Defender. It has also created comic books and a downladable video game.
Voltron was given an extra season after Beast King GoLion ended. This created the villainess Queen Merla, Queen of Darkness, who briefly married Lotor. Additionally, there were heavy hints that Allura and the Voltron leader Keith were romantically interested in one another, which is more or less confirmed in Voltron Force.
Voltron actually did better in North America than Beast King GoLion did in Japan, so Toei, the company that created Beast King GoLion sold their rights to Beast King GoLion to World Events Productions.