Creation

Julian Olsen was created by Matt Fraction and Steve Lieber as an antagonist for the Superman's Pal Jimmy Olsen comic series.

Being Mister X

Julian Olsen and Lex Luthor continued the grudge of generations between the Olsens and the Luthors. When Lex wanted to tear down the Metropolis Monarch, Julian opposed him. He had realised, that the infrastructure beneath the Monarch monument would be valuble for Luthor. He would gain a huge advantage by replacing and controlling them. Lex engineered events, so that Jimmy Olsen, Julians younger brother, would accidentally destroy the monument.

This was the last straw Julian had. Between his investments and cleaning up after Jimmys misadventures, Julian had depleted the family fortune. When he realized that Jimmy never touched his trust fund and his death would redirect the funds backt to the rest of the Olsens family, Julian disguised himself as Mister X and put a contract out on Jimmys life. He eventually discovered the truth and confronted his brother.

Julian tried to flee Metropolis but was cornered at the airport. Julian boasted about everything he'd done and pulled a gun on his brother. Before he could pull the trigger Porcadillo, a minor villian of Metropolis, tackled him tackled him down. Julian was arrested for his crimes and Jimmy reported the story in the The Daily Planet.