Dickon is the younger brother of Samwell Tarly. He became their father Randyll Tarly's heir after he disinherited Samwell by forcing him to join the Night's Watch.
Dickon is athletic, a skilled hunter and excellent swordsman, though not particularly bright and also quite arrogant and condescending. Naturally gifted at martial endeavors, he is his father's favorite child. After Randyll Tarly banishes his old brother Samwell Tarly to the Wall, he designates Dickon as the heir to Horn Hill and the Valyrian steel sword Heartsbane, which has been in the family for five hundred years.
When Samwell Tarly returns to Horn Hill with his "lover" Gilly and "their child" Little Sam, Dickon and his father Randyll are out hunting. Later at dinner, he is cordial but cool towards his older brother and Gilly. When Sam asks him whether they're eating the deer that he and Randyll hunted, Dickon replies that what they're eating was in fact last week's haul and that they did not have time to cure today's catch. He also engages in dinner table conversation with Sam about hunting beyond the Wall. Sam tells him that there are no deer and elk to hunt but only rabbits.
After Gilly tells the hosts that Samwell killed a White Walker, Dickon expresses amused disbelief and claims that White Walkers are just a myth. He is present when Randyll tells Sam that he will find work for Gilly as a servant and foster Little Sam as his grandson, but that Samwell is no longer welcome at Horn Hill. Undaunted, Sam takes his "family" away and also steals the family heirloom Heartsbane.
Dickon attend Cersei Lannister's court of Reachmen, along with his father, who mentions the fact that the Dothraki and Unsullied will attack Westeros during Daenerys Targaryen's invasion. Jaime, wanting to get Randyll on his own, accidentally calls Dickon "Rickon", before privately requesting an audience with Randyll.
Dickon eventually follows his father's decision to forsake the Tyrells and, together with Randyll, becomes part in the Lannister war efforts against the Tyrells which culminates in the Lannister army conquering Highgarden. During this battle, Randyll functions as a general of the Lannister army, with Dickon by his side.
On the ride back to King's Landing, Jaime accosts Dickon, again calling him "Rickon". Dickon corrects him, and Bronn laughs at his name, to Dickon's irritation. Jaime inquires how Dickon feels about conquering Highgarden; Dickon initially claims it was glorious, but once Bronn reminds him that Randyll is out of earshot, Dickon shows some regret, saying he knew many of the men there and had hunted with them.
Jaime consoles Dickon, agreeing that they did not deserve to die, but Olenna betrayed her Queen and as a result Highgarden had to be taken. Dickon also notes that the carnage smelled worse than he expected, something Bronn claims he learned in infancy. Later, the Lannister/Tarly army is ambushed by a Dothraki Khalasar commanded by Daenerys Targaryen, who is flying on Drogon. When Drogon blasts a hole in the army's formation with his fire, Dickon looks on in horror at the burning soldiers.
Despite fighting fiercely, the Westerosi forces are swiftly overwhelmed by the combined cavalry and dragonfire attack, and the battle soon becomes a rout. Dickon saves Jaime from a Dothraki warrior by stabbing the warrior in the back. Jaime nods at him in gratitude.
After the battle, Dickon and his father are among the prisoners of war lead to Daenerys for an ultimatum. She offers the choice to bend the knee, or be executed. After Randyll refuses, Dickon joins his father in denying her as their Queen, despite both his father and Tyrion protest since his death will mean the near extinction of house Tarly. Daenerys subsequently sentences them to both to death by dragon fire. At her command, Drogon obliges and burns father and son alive despite Tyrion Lannister urging Daenerys to show Dickon and his father mercy by putting them into dark cell to make them change their mind.
Second son to Randyll Tarly, Dickon had interests that were more in line with his father’s. This trait endeared him to Randyll, who forced Sam to renounce his birthright so that Dickon would inherit Horn Hill. Dickon accompanied his father to the capital when Cersei summoned her noblemen, and was killed when he refused to bend the knee to Daenerys after the battle by the Blackwater River.