In Father of the Dead, Jaqelos is employed by Ethan Dragen to kill his deranged nephew, Lucius Dragen, who has recently gone into exile. On the way to Lucius' last known location, Jaqelos gathers information on him and becomes greatly interested about him, to the point that it becomes a near-obsession.
After killing Lucius Dragen, Jaqelos mysteriously disappeared, never to be seen again.
Little is known about Jaqelos' early life. He was born in the free city of Tyrosh to the Eranelion family, an old and powerful aristocratic family that secretly rules Tyrosh behind the curtains. When he turned eighteen, Jaqelos joined the Golden Company, one of the largest and most skilled sellsword companies in the Free Cities, and was simultaneously disowned by his family for this. Jaqelos became an assassin for the Company, tasked with executing various political murders for a sizeable amount of coin.
His last contract fell heavy on him. Details are unknown, but the last assassination he committed left a deep mental scar in his memory and he later retired from the sellsword life. However, being a hired blade for so long, the desire to return for one last contract increased and he was unable to return to a normal life and settle down.
Following his retirement, Jaqelos' wife left him and took their young son with her. They hardly spoke to each other until Jaqelos agreed to the separation without any reluctance. Jaqelos was left with only the house in Tyrosh, which he soon sold to board a passage to Westeros.
Father of the Dead: Part 2
Jaqelos sits at a tavern in the city of White Harbor, while reminiscing about his life as a sellsword and hired cutthroat. While sunken away in his thoughts, he is approached by two Dragen man-at-arms. They hand him a sealed letter and tell him that if he still wants to redeem himself and carry out one last contract, he should pay a visit to Snake Mount. The two men leave while a confused Jaqelos unseals the letter and reads its content. After staying at the tavern for two days, all the while contemplating about the letter from Snake Mount, he decides to go to Snake Mount and seek out his mysterious contractor.
At Snake Mount, Jaqelos is welcomed by the steward who tells him that "Lord Ethan" has expected him. Jaqelos follows the steward into a grand feasting hall where he is greeted by Ethan Dragen, Ser Duncan Catell, and Maester Vahaelor. Ser Duncan asks him if he is truly the famed "Jaqelos of Tyrosh" and if he once worked with the Golden Company. Jaqelos verifies that he indeed worked with the Company but refuses to tell them that he worked as a hired assassin and that he - on multiple occasions - indeed murdered high political targets for large amounts of gold. Ethan observes Jaqelos thoroughly and carefully and then invites him to eat with them at the table. After doing so, Ethan tells Jaqelos that - before he became the Lord of Snake Mount - his nephew ruled the House. According to Ethan, his nephew was a ruthless and feared individual who liked to cannibalise his own subordinates. He also tells him that he has suffered multiple traumatic experiences in his childhood which ultimately lead to his insanity. Eventually, the former Lord of Snake Mount became so mad, that he was forced into exile after nearly surviving a duel with Ethan. He reveals to Jaqelos that his nephew's name is Lucius Dragen and asks him if he has ever heard that name before, to which Jaqelos admits that he has "heard rumours" back in White Harbor. Ethan quickly dismisses these rumours and tells him that they are all true. After the feast is over, Ethan gives Jaqelos his mission; he will arrive at Volantis by boat where he will be received by a contact of Ethan's. After handing Jaqelos valuable information and documents on Lucius and his past, he is to sail up the Rhoyne river in a small boat owned by the Golden Company called "the Valorous", captained by the eponymous "Captain". Jaqelos will then continue his journey on the Qhoyne and then pick up Lucius' trail onland, and find out where he is. After finding out where he is, Jaqelos has to assassinate him. Ethan tells Jaqelos that he is to tell no one of this mission, not even his own relatives.
Eventually, Jaqelos accepted the contract and sailed to Volantis immediately the day after. At the harbor, he is received by a contact of Ethan named Illeso. Illeso gives Jaqelos some more information on Lucius and says that he has lived in Braavos for almost half a year, before he left. He hands Jaqelos a bunch of documents and transcripts and then tells him to head to the northern port, where the Valorous will be waiting for him.
On the Valorous, Jaqelos meets the captain, and his crew: Zoratto, a dothraki warrior who was banished from his khalasar when he refused to kill his own brother, even though Khal Moro, his khal, ordered him to do it. Rhaelyx Velaryon, a member of a lesser branch of House Velaryon who wanted to pursue a life of adventure and romance, and Tycharo Fynyr, a twelve year old stray hailing from the slums of Lys who was caught trying to illegally board the Valorous.
On the way to Lucius, Jaqelos reads the documents and transcripts given to him by Illeso. He learns that Lucius, as a child, became stranded in the Northern wilderness almost twenty years ago which resulted in him being left emotionally and physically scarred for life.
Jaqelos and his men stop at Qohor to resupply and rest for a few days. They are greeted by Magister Aeren Nestaris, a major merchant-lord in the city. Once there, however, they experience strange events and feel very uncomfortable being in the city. Eventually, they learn that a grand harvest festival is being held where humans are being sacrificed to the Black Goat, a major deity in Qohorik religion. The Captain, Rhaelyx, and Tycharo are abducted by the Horned Men, a priesthood devoted to the Black Goat, to which Nestaris is the high priest. Supposedly, a time of strife has struck Qohor and in order to please their deity, the Qohorik sacrifice newly arrived travellers to the Black Goat. Jaqelos and Zoratto make an attempt to save the crew and successfully flee the city.
While on the Qhoyne, Jaqelos becomes gradually more intrigued about Lucius and his past. He reads the documents thoroughly and the more he understands, the more he wants to confront him.
The crew eventually arrive onland and have to continue their journey on foot through the Dothraki Sea, much to Zoratto's dismay. Zoratto admits that his khalasar is still out for his blood after he left his family to pursue a life as a mercenary. He is afraid that - if any other khalasar finds him - they will behead him. After journeying through the Sea for a few months, they are eventually ambushed by a group of bloodriders belonging to Zoratto's former khalasar. One beheads Zoratto and an other impales the Captain with a spear. When Jaqelos successfully kills the bloodriders, he gives Zoratto and the Captain a proper burial.
Jaqelos, alongside Rhaelyx and Tycharo, eventually arrive at the Kogathi Highlands after a time. They fabricate a crudely wooden raft and sail on a river to Lucius' last known location. Eventually, they arrive at a Yi Tish temple dating back to the time of the Golden Empire. They are welcomed by a visibly deranged and manic person, calling himself Gaige. Jaqelos remembers him as Vahaelor once told him that they sent another assassin before Jaqelos to kill Lucius. Gaige was a deserter from the Lannister army following their defeat at the Battle of the Yellow Fork. Gaige was given an opportunity to be pardoned if he were to kill Lucius. However, he refused to kill him after spending a few days alone conversing with him. As Jaqelos assumed, Lucius brainwashed him.
When Jaqelos asks if he could speak to Lucius Gaige replies by saying that "no mortal man speaks to the Lord of the Hunt, only divine or semi-divine beings like himself". When Jaqelos asks where he is, Gaige claims that he is out hunting with his men.
A few hours later, Jaqelos orders Tycharo and Rhaelyx to stay behind on the raft and if he's not coming back in 24 hours, they should go to Kogath and get help, preferably an army. After Jaqelos returns back to the temple to face Lucius, he becomes surrounded by hundreds of Lucius' followers and they truss and kidnap him. Jaqelos is brought before - what he observes as - an old man, probably in his sixties, with a plump belly and a bald head. He has a long black beard extending all the way to the center of his chest with grey plucks of hair. As he talks to the man, he quickly comes to the conclusion that this "old man", is in fact Lucius himself. Lucius quickly confirms that Ethan must've send him. He admits that Ethan has sent multiple assassins to him as well, but he has either killed them or turned them over to his side, through, what he calls, "brilliant persuasion".
After a few days, Jaqelos is tortured and tied to a pole in the middle of a monsoon downpour. Lucius walks up to him but does not utter a word. He walks to the back of Jaqelos and puts the decapitated head of Rhaelyx on his lap. A disturbed and horrified Jaqelos screams at the sight of him.
In the morning, Lucius visits Jaqelos again in his cage, surrounded by hundreds of children. Lucius reads the documents and letters Ethan gave to Jaqelos out loud, which upsets the captive mercenary. Lucius eventually says that Jaqelos will be freed from his restraints and allowed to walk free, but he will be kept under constant surveillance to ensure that he does not leave the temple. When Jaqelos is freed, he struggles to stand up to walk out of his cage and instead falls to the ground and sleeps.
After being in the temple for a few weeks or months, Tycharo eventually approaches Jaqelos and tells him that he could not find an army for him, but he was able to smuggle a dothraki arakh for him. Jaqelos thanks him and says that Tycharo needs to hide and ready the raft for the night. When Tycharo leaves, Jaqelos hides the arakh and waits for the night to descend upon the Highlands.
During a grand feast being held by the Highland natives to honour their god by slaughtering a cow, Jaqelos seizes the opportunity to infiltrate Lucius' room. Once inside, he slays Lucius with the arakh and when he finally dies, Jaqelos succumbs to the stress and trauma.
When he walks outside, he holds Lucius' decapitated head in front of him to show it to the tribe. They eventually bow before him and lay down their weapons. When Jaqelos walks with Tycharo to the raft, he leaves the temple, and they are never seen again.
Jaqelos is a nihilistic and cynical man with a dry and sarcastic sense of humour. He does have a certain degree of honour that keeps him from abandoning unfinished contracts. Jaqelos is convinced that there is no such thing as "true evil" or "true good"; he views every man as both good and evil. However, after learning about and confronting Lucius Dragen, this ideology changed dramatically which convinced him that true evil does exist, but is not inherent or fundamental with humans; there is always an ulterior motive or external factor that contributed to one's ascension to evil.