Lucius Malfoy was a Death Eater who appeared from season 1 until 9 in the series.
When Voldemort was defeated when Harry was a baby, Lucius Malfoy begin working for the Ministry Of Magic. He was the nemesis of the father of the Weasley family. However, when Voldemort returned, Malfoy returned to his former master. Due to that the Minister Of Magic trusted him, he dind't believed he was a Death Eater.
It was believed that Malfoy's child was Draco Malfoy, however he was actually the son of Lord Voldemort. Lucius had never known that this was true and loved his son. He was a very rich man due to his work and that he helped Voldemort. However, Malfoy's son, Draco, first wanted to be a Death Eater, but later betrayed his parents and dind't want to have to due anything within the conspiracy.
Lucius was married to Narcissa Malfoy and she came from Lestrange family, Bellatrix Lestrange was also a death eater.
Lucius's role within the conspiracy is not quite revealed, but he was one of the most helping servers of Voldemort. Narcissa was also a death eater, but she came to the good guys and was subjected to experiments by Lucius and Voldemort in order to create a human like militairy soldier. However, Narcissa escaped after the third torturous test and was placed in a hospital, but re-kidnapped again by Lucius for the Dementor deal at Gringotts bank. He and all the other death eaters, except for Antonin Dolochov and Voldemort where killed by a group of bombers in 1998.