Aaron Siegel is an American scientist who founded the SCP Foundation in the 1800s. Siegel would eventually retire from this position and became O5-1. He founded the Foundation after a mission in The Factory, and meeting then killing The Factory’s founder, James Anderson. The Factory would later be called SCP-001, and Anderson would be known as UTE-0561-Venice Green. Siegel would also go on to kill the Gate Guardian using The Spear Of The Nonbeliever. He does not need to sleep, and is immortal.