Short answers, pulled from the story.
Marcus Didius Julianus entered the world on the 29th of January 133. His father was Quintus Petronius Didius Severus from Mediolanum and his mother was Aemilia Clara, a North African woman of Roman descent.
The Praetorian Guard sold the throne to the highest bidder after Pertinax died on the 28th of March 193. Julianus offered 25,000 sesterces per soldier which exceeded the 20,000 sesterces promised by Titus Flavius Claudius Sulpicianus.
Julianus reduced silver content in the denarius from 87% down to 75% upon accession. This devaluation nearly matched the adulterated amount present during Commodus reign and restarted economic instability trends.
Septimius Severus marched on Rome and the Senate sentenced Julianus to death on the 2nd of June 193 AD. He ruled for only 66 days before dying in the palace by a soldier's hand.
The Senate passed a damnatio memoriae motion condemning his legacy completely because he bought his position rather than acquiring it through conquest or succession. His blatant purchase of the throne shattered illusions of normalcy remaining in the Roman state.