Simoun is the main character in Jose Rizal's two El Filibusterismo novels. As Crisostomo Ibarra (which is his real name), he is the main protagonist in Rizal's first novel, Noli Me Tangere. In the first novel, he was idealistic, believing that social reforms can bring the end to the social cancer plaguing the Spanish-ruled Philippines. In Rizal's second novel, he returns as a rich jewelry salesman, Simoun. He is known to be the influential in the Spanish colonial government in the Philippines and has links to the Captain-General. He seeks to ignite the sentiments of the Filipinos, so that a revolution may arise.
Being the conflict catalyst in El Filibusterismo, aside from having a more hostile and radical ideology, Simoun is arguably the main antagonist of the second novel, in contrast to his more heroic role in Noli Me Tangere
Crisostomo Ibarra returned as a rich jeweler under the name of Simoun. He abandoned his idealistic views after going through tragic events in the last novel. He believes that obstreperous and violent revolution is the only way to bring about end to the abuse of the Spaniards, especially the clergy. He intends to do this by influencing the Captain-General to make erroneous decisions that would lead to further suffering of the Filipinos. He believes that doing so would open their eyes of the truth and start a revolution. His other goal is to free Maria Clara from the convent.
Maria Clara died while serving in the convent which drove Simoun to further pursue his plans.
His true identity was discovered by Basilio, the protagonist in the novel and a graduating student of medicine who has views similar to Simoun's former self. Simoun managed to sway him to his side after Basilio going through his own set of tragedies.
At the eve of the wedding of Paulita Gomez and Juanito Palaez, Simoun asked Basilio to take him to his laboratory and revealed that he plans to give the newlyweds a kerosene lamp with explosives as a gift during them reception at the house of the late Captain Tiago. When the lamp explodes, it will kill all people within its proximity including influential political and religious leaders. Simoun's plot was foiled by Isagani, who threw the lamp into the river. Basilio, after confronting his doubts, warned his friend Isagani about the plot.
Simoun was revealed to be responsible and was searched by the civil guards. He was shot by a civil guard during his escape and sought refuge at Father Florentino's house. He revealed his identity to the priest and asked him why did his plot failed even though he has good intention to free the Filipinos from oppression and why God has forsaken him. Father Tolentino replied that his plan failed because he was driven by revenge and that God did not forsaken him. Before his death, Simoun accepted Father Florentino's explanation and has realized his wrongdoings.