Ethan Clark was a Gotham City businessman.
Clark was an estate banker, rarely taking financial risks. To shield himself from any mistakes, he turned to the "mystic" Nostromos. Nostromos recommended against certain investments and all his revelations came true: a cave-in at the Zanza mine, a fire at the Karobi oil field, and lastly Nostromos advised against going on a gambling cruise—rightly so, because the ship sank under suspicious circumstances.
His daughter Lisa was a vocal critic of his trust in Nostromos, as she believed he was making his own predictions come true. Lisa was appalled when her father inducted their friend Bruce Wayne into the society. On their way to their first meeting, he informed Bruce of Nostromos' greatest prophecy yet: economic downfall in the West akin to the Great Depression. At the advice of Nostromos, they had set up a superfund which would protect the Brotherhood from the ill effects and enable them to rebuild their lost fortunes. To avoid too much suspicion, Nostromos allowed Clark and Brotherhood members voting rights in the superfund.
That night, Nostromos convinced him that the downfall was near; the next morning the first thing he would do was put all his money into the superfund. But Nostromos was not fully pleased: the entire superfund would have to be converted into gold bullion. When Clark refused, stating that the Brotherhood would have to be notified first, Nostromos revealed his true self: he would kill Lisa if he did not sign the papers. After Clark succumbed, he was tied him up to die when the building exploded.
Batman broke in, and after defeating Nostromos, he got Lisa and her father to safety.
After Lucas and Carl Fowler were arrested, Ethan Clark was seen with Bruce, commenting how his greed clouded his judgment. Bruce was sympathetic, quoting a line from Julius Caesar; "The fault, dear Brutus, is not in the stars, but in ourselves".