It is Valyrian steel longsword with a black blade.
Ser Jon Roxton wielded the blade during the Targaryen civil war known as the Dance of the Dragons while fighting for King Aegon II Targaryen and the greens. During the Battle on the Honeywine in 130 AC, he used it to deliver a fatal wound to Lord Owen Costayne. Jon knighted Titus Peake after the battle for valor in the field. He presumably used Orphan-Maker for the ceremony.
Later that year, Jon used Orphan-Maker to split in two Lord Footly in the aftermath of the First Battle of Tumbleton and Hugh Hammer during the second battle. Jon was immediately killed by Hugh's men in retribution, however.
The sword came into the possession of another green commander and the father of the late Ser Titus, Lord Unwin Peake. When Peake became Hand of the King during the regency of young king Aegon III Targaryen in 133 AC, he drew Orphan-Maker, declaring that unlike the previous Hand, the blind and crippled Ser Tyland Lannister, he could still wield a sword.
The sword's current whereabouts are unknown.