Shinzon was a half arsed clone of John Luck Pickerd (later Jean-Luc Picard), despite the fact there was about 230 years difference between the two, Shinzon was supposed to infiltrate Starfleet somehow and do some things for the Romulans.
However once Jean-Luc scored with a chick at Starfleet academy, giving him the confidence to continue his career, Shinzon was sent packing to the Reman 'Fuck me in the arse' prison/mining colony (though we all know what the Remans were really mining).
Later he and his Reman molester's led a coup against their Romulan opressors, killing off the Romulan Senate by giving them a techno light show worthy of Ibiza. The Romulan's were so tripped out they started raving till they all died of seizures. This light show was generated by a Thalaron weapon, which Shinzon first tested on the Domination's home planet, ending the Domination War, don't ask how he made it to the Gamma Quadrant, he just did.
Shinzon and his main Reman love, his Viceroy then took over power, and invited Picard to come to Romulus where he (Shinzon) displayed some total bi-polar behaviour (see Kathryn Janeway) first warming to Picard, then hating him (Picard later in his de-breifing to Starfleet said Shinzon was too young for him, and that he(Picard) was straight and not bi-curious at all).
So Shinzon got pissed, not only with his oily coloured bondage geddup, but with Picard's rejection, and launched his super duper, most motherfucking bad-arse ship (the Scitimar) to kick the crap out of the Enterprise-E, which it did, till Picard thought it would be a good idea to play chicken with the Scitimar, while this was happening, Shinzon's STDs (courtesy of Vicerory) were starting to take their toll. Picard beamed over to the Scitimar to destroy it's mega, ultra, disco, e-popping, Darude pumping, Ibiza quality Sound System, which Shinzon was to launch against Earth much as he did against the Romulans.
However, in a final move of desperation, Shinzon tried to bitch slap Picard, only to wound up poleaxed in the stomach, distraught he hadn't had a large pole shoved in the place he'd most loved it to, he died. Oh, and coupled with the destruction of the Scitimar due to hebot Data destroying the onboard mounted Thalaron generation, that kinda finished him off.
Shinzon bidding one final farewell to the love of his life (after his Viceroy) 
Oh yeah, and the STDs also killed him too, but death due to being distraught make's it sound more emotional.
Shinzon was played by Tom Hardy, who was really Patrick Stewart from the past. Marty McFly in 1955 decided to pick up Patrick Stewart and take him into this era, for no good reason.