Aegor Rivers was the second of Aegon IV's acknowledged bastards, born in 172 AC to Barba Bracken and raised, by the queer arithmetic of that court, alongside the half-siblings whose throne he would spend his life trying to take from them. Where Brynden Rivers chose the dragon that already wore the crown, Aegor chose the one his father had named — Daemon Blackfyre, given Aegon the Conqueror's own sword Blackfyre on his deathbed, and with it a claim half the realm found more convincing than blood alone allowed.
That choice cost him the field at Redgrass in 196 AC, where Daemon died to his half-brother's arrows and the First Blackfyre Rebellion died with him. Aegor did not. He fled across the narrow sea with what remained of Daemon's household, and for the four decades left to him he never set foot in Westeros again — not from any recorded oath, but because no opening the Blackfyre cause found in his lifetime ever looked survivable enough to risk it.
What followed was the Golden Company: every Blackfyre exile the rebellion left scattered across the Free Cities, gathered under one banner in 212 AC and paid, fed, and drilled well enough that "the Golden Company never breaks a contract" became a boast the market believed. Aegor led it for three decades, backing further Blackfyre risings he did not always survive to see finished, and died in the Disputed Lands in 241 AC — never having set foot on a Westerosi battlefield again, but close enough to one that the company kept marching without him.