The Joranumite Conspiracy was a rebellion (or initially a pseudo-rebellion) against the rule of Emperor Cleon I. It is mostly significant because it occured at the peak of Hari Seldon's early work on Psychohistory, and in fact, while the initial rebellion was quelled when Eto Demerzel was First Minister of the Empire, the remnants of the Conspiracy regrouped and launched a serious attempt to kill Hari Seldon while the latter was First Minister. It was during that assasination attempt that Emperor Cleon I died, killed by a disgruntled gardener who had nothing to do with the main plot.
The Joranumite Conspiracy started around 12,--- GE, after Hari Seldon returned to Streeling University from The Flight. At the time, with the blessing of Eto Demerzel, he was working intensely at developing psychohistory. Meanwhile, Jo-Jo Joranum, a charismatic politician playing the role of a Periphery inhabitant, began preaching equality among Trantor sectors.