Visenya Targaryen was Aegon I's elder sister and, per the Valyrian custom the family kept even after fleeing Valyria, his wife as well — a dragonrider in her own right astride Vhagar, second-largest of the three dragons that made the Conquest possible, and a swordswoman the chronicles credit with more skill than either of her siblings ever claimed for themselves. She carried Dark Sister, one of the Seven Kingdoms' Valyrian steel blades, throughout a war and a reign her more celebrated brother could not have managed without her.
Tradition holds that it was Visenya who pressed Aegon to found the Kingsguard after an attempt on his life during the Conquest's early fighting — seven sworn knights, answering to no house but the crown's, a number the Citadel notes may owe as much to the Faith's seven-pointed star as to any tactical calculation. Whether the idea, or the urgency behind it, was truly hers is a claim the surviving record cannot fully test; it is simply what got repeated often enough to stick.
She outlived Aegon by seven years, a formidable and rarely comfortable presence at the court of her nephew Aenys I and then her own son Maegor, whose ascent to the throne in 42 AC the less charitable chroniclers have never stopped murmuring she engineered. She died in 44 AC while Maegor was away on campaign — the last of the three Conquerors to draw breath, and, if the rumors are to be credited at all, very possibly the one who shaped the realm's early decades most.