Lucan Blackgard is a recurring character in the fourth, fifth and sixth seasons. He is a son of Lord Trevyr Blackgard and his deceased wife, Lady Laenah Blackgard. He is the younger brother of Dyron Blackgard and older brother of Eddin Blackgard. He is married to Jenelyn Harrigon. He is considered a weakling among House Blackgard.
Lucan is the thirdborn son of Lord Trevyr Blackgard. Trevyr is the Lord of Ebonheart and Lord Defender of the Stormlands. Lucan is considered to be weak and unable to lead. He was kept out of most of House Blackgard's affairs and this frustrated him multiple times.
Trevyr sends Lucan to King's Landing to act as a representative of House Blackgard to the Crown. Lucan oversees all King's Landing activities that are involved with House Blackgard or The Borderlands. In an attempt to gain control of the Borderlands and gain House Blackgard as allies, Cersei Lannister offers Lucan a position on the Small Council, but he refuses, being able to see right through her. However, Lucan later reconsiders and accepts, using it as an opportunity to learn about Cersei's other activities. He is able to use his position to subtly block Cersei's attempts to gain a foothold in the Borderlands or within House Blackgard.
After Dyron Blackgard's death, Lucan receives word that his father, Trevyr Blackgard, has disinherited Lucan, refusing him to become the Lord of Ebonheart. Lucan, angered, stays in King's Landing and does not return to Blackgard to attend Dyron's funeral.
Lucan marries Jenelyn Harrigon. This strengthens House Blackgard's relationship with House Harrigon even more. Knowing that Lucan was considered the weakling and the most cowardly among lord Trevyr's sons, Jenelyn's father lord Rickard had concerns about Jenelyn's safety, sending Ser Lannord and Lancen Storm with them on their way to King's Landing, where they remained with them until Ser Rolland Hollard takes care over Jenelyn. After a year of marriage, Jenelyn announced her pregnancy and that Lucan would become a father. This does nothing to reconcile Lord Trevyr and Lucan. Lord Trevyr does however right a letter directly to Jenelyn congratulating her. Jenelyn later gives birth to Mercyl, but yet again, it did nothing to reconcile him and his father.
When Cersei Lannister initiates the Destruction of the Great Sept of Baelor, Lucan is preparing to attend Cersei's trial when he is approached by Roman Mercer, who has newly returned to King's Landing. Lucan orders him to stand aside. However, Roman says that he can't do that and refuses to move. Realizing that Roman has come to kill him, Lucan casually grabs a candle holder and uses it to fight Roman. They both manage to disarm each other, but as Lucan runs to get his sword, Roman manages to stab him in the gut. After falling to the ground bleeding, Roman cruelly mocks Lucan, saying that he sent men to kill his wife and son as well. He leaves Lucan's room with the door open. As Lucan crawls out of his room to try and warn King Tommen, he dies of blood loss. His death initiates an open rebellion between the Iron Throne and House Blackgard, who have since openly declared to support to House Targaryen's bid for the Iron Throne.
Following the destruction of the Great Sept, Jenelyn is strangled to death by the members of the Blackwatch. Their son Mercyl is taken by Ser Rollan out of King's Landing and taken to Hornworth, where he is taken into the care of his "uncle" Ser Ardrew Ashes.