Lotho was the son of Lysandro Rogare. He had five trueborn brothers: Lysaro, Moredo, Drako, Fredo, and Roggerio; and three trueborn sisters: Larra, Lysara, and Marra, as well as sixteen bastard siblings.
When his sister Larra came to King's Landing as the wife of Prince Viserys Targaryen, Lotho, Moredo, and Roggerio came with her. Lotho and Rogerrio were fluent in the Common tongue, although Moredo was not. Lotho set about establishing a branch of the Rogare Bank of Lys atop Visenya's Hill. With the Rogares growing in power late in 134 AC, it was feared by some that they would soon rule Westeros as well, though Archmaester Gyldayn notes that suspicion was largely caused from them being foreign. However, it is known that Lotho used gold to buy friends at court.
After Lotho's father Lysandro "the Magnificent" drowned, his brother Lysaro inherited the Rogare Bank, quickly running it dry with debt and embezzlement. Lotho attempted to depart King's Landing before he could be punished, but was arrested by the Commander of the City Watch, Ser Lucas Leygood. Because of Lotho's relationship to Prince Viserys's wife, he was imprisoned in the Tower of the Hand rather than the black cells.
After the events of the secret siege, Lotho was tried, accused of fraud and theft, and found guilty. Lord Torrhen Manderly gave him the chance of joining the Night's Watch or losing his right hand like a common thief; as Lotho was left-handed, he chose the latter. He was then taken up by Lady Samantha Tarly, paramour of Lord Lyonel Hightower, who had him establish the Bank of Oldtown.
—Lotho, to Torrhen Manderly