Pelleas is the supposed son of Daein's King Ashnard in Fire Emblem: Radiant Dawn, making him heir to the kingdom's throne. He is brought to the attention of the Dawn Brigade by Izuka, who had previously worked under Ashnard during the events of Fire Emblem: Path of Radiance while conducting inhumane experiments on laguz. Proof of Pelleas's lineage is in a mark on his body that is like that of a Branded; the offspring of a beorc/laguz parentage. Ashnard, in fact, did father a son with Almedha, a dragon laguz of the royal black dragon bloodline, but the child was spirited away and never seen again. Pelleas grew up in an orphanage, and when Izuka came across him in his travels, he recognized the young man as Ashnard's son.
While Pelleas steps up to the challenge of becoming a leader of the resistance movement, he is not talented at motivating crowds, and he quickly takes a backseat to Micaiah, the "silver-haired maiden" that had managed to win the hearts of Daein's people and became a symbol of hope for the oppressed. However, Pelleas is not bitter about his plight, as he recognizes that he has faults and weaknesses that must be overcome. He aids the Dawn Brigade where he can, but keeps Izuka at his side as an adviser. His mother Almedha also constantly hovers nearby and obsessively guides him when able.
After the Dawn Brigade and the rebel forces drive Begnion's occupation army to defeat, Pelleas becomes king and signs a treaty with Begnion to formally declare the conflict at an end. Or at least, that's how things appeared from a distance. In reality, Pelleas, as well as the rest of Daein, had been duped by both Begnion as well as by Izuka, who had been serving Begnion as a double agent. The treaty that Pelleas signed was in fact a blood pact; a magical document that requires Pelleas to follow the orders of Begnion's senate. If at any point the senators involved in the conspiracy feel hat Pelleas isn't living up to their desires, they will activate the pact's penalty; the death of every Daein citizen.
Trapped, Pelleas is forced to do as the senators command and sends the Daein army to assist Begnion in their war against the laguz. However, after speaking with Micaiah and relating the truth to her, he diligently searches for a means to nullify the pact. Through his research, he comes to the conclusion that if the signer of the pact is killed by a third party, the pact should be nullified. He then makes a plea for Micaiah to kill him. At this point, the player may either choose for Micaiah to end Pelleas's life, or request the Daein officer Tauroneo perform the act instead.
In either case, however, the pact is not nullified. Rather, the pact's brand is transferred to Micaiah. The pact remains in effect until the actual blood pact document is destroyed after it is taken from Lekain, the senator that authored the pact.
In a second playthrough of the game, Micaiah is given the option to refuse Pelleas's request, and after further consideration, Pelleas believes that the pact could also be thwarted if Lekain were to be killed instead. Not willing to give up, he then becomes a playable character of the Dark Sage class.
In Part 4 of Radiant Dawn's story, Pelleas joins with Tibarn's Hawk Army and travels with it to the Tower of Guidance. Along the way, the Hawk Army encounters Izuka, who has holed up in a swampland and is accompanied by packs of his Feral Ones. Upon being confronted, Izuka imparts the truth; Pelleas is not in fact Ashnard's son. He was merely being used by Izuka, who had been promised rewards by Begnion's senators if he did as they asked.
Should Pelleas enter the Tower of Guidance at the game's end, he can enter battle with both the senator Lekain and Sephiran, the traitorous Prime Minister of Begnion. In confronting Lekain, Pelleas states that he has grown stronger because of his struggles and his friends. The pact that had proven such a burden is nullified with Lekain's death and the document's destruction. In facing Sephiran, Izuka's story is confirmed; Sephiran also informs Pelleas that it was he, not the senators, that plotted the blood pact, all for the sake of instigating war and awakening Ashera.
Following the war, Pelleas steps down from Daein's throne in favor of Micaiah and faithfully serves the new queen as a member of court.
The Spirit Charmer
Pelleas is a spirit charmer; a beorc that allows a spirit to enter his body and to feed off of his soul in exchange for enhanced magical power. Due to the risks involved, spirit charmers are exceedingly rare. Their deals with spirits also leave a mark on their bodies. These marks are similar to the marks worn by the Branded, and as a result, it is easy for others to confuse a Branded for a spirit charmer, or vice versa. It is likely in part because of Pelleas's mark as a spirit charmer that Izuka was able to use him as a pawn and pass him off as the son of Ashnard, whose own son is a Branded. Ironically, Ashnard's true son, Soren, spent the early years of his life in the care of an old man that incorrectly assumed he was a spirit charmer due to his brand.