Star Trek Nemesis

At the beginning of the movie, we first see a congregation of Romulan leaders in the Romulan Senate. At the forefront are a pair of Romulan commanders telling the senate to vote in favour of an alliance with Shinzon of Remus (Tom Hardy), the supposed leader of the Remans who becomes Picard's nemesis later in the story. After the Senate refuses, the two commanders and a member of the senate excuse themselves, leaving behind a mysterious object that soon sprays green particulates across the room which cause the senate members to literally turn to stone and fall apart.The next scene shows the wedding of Commander Will T. Riker (Johnathan Frakes) and Counselor Diana Troy (Marina Sirtis) in which Jean-Luc Picard (Patrick Stuart) makes a touching speech announcing that unfortunately Riker is moving on to Captain the USS Titan and that Commander Data (Brent Spiner) will be promoted to First Officer.The plot begins to thicken as, after returning to active duty aboard the Enterprise, a positronic signature is detected on a nearby uncharted world close to the Romulan border. As these signatures have only been known to eminate from Androids, Picard, Worf (Michael Dorn) and Data travel down to the Planet to investigate upon a new larger shuttle containing an advanced type of Dune Buggy. In the course of scouring the planet's surface, parts of one functioning android are found scattered across a great distance. After finding the head (the final piece), the trio are attacked by the native species in several vehicles with Machine gun emplacements on top. The trio flee back to the ship in the Dune Buggy while firing at the alien aggressors with a powerful laser cannon fitted to the back of the vehicle, only to find it surrounded. Using a remote control, Data pilots the ship away from the aliens, much to the aliens' surprise, and to the edge of a cliff where Picard daringly pilots the vehicle into the open back of the ship.Back aboard the Enterprise, the droid is reassembled and identified as a underdeveloped prototype version of Data called B4 (also played by Brent Spiner). After doing so, there is a touching scene between Data and the Android in which Data tells him that they are brothers. Meanwhile, Picard is contacted by Star Fleet command, in particular Admiral Janeway who has recently returned from the Delta Quadrant. She tells him that his new orders are to travel to Romulus for mysterious peace talks with the New Praetor, Shinzon of Remus, who is also relatively unknown by the Federation, apart from his exemplary military command record.At Romulus, the crew wait for about 17 hours to be hailed by the new Praetor. Eventually, a extremely heavily armed ship decloaks of the front bow of the Enterprise; this ship is later referred to as the Reman Warbird Scimitar and is armed with 52 disruptor banks and a large of Photon Torpedo bays. The crew, in partial shock at the superior nature of the Scimitar in comparison with the Enterprise, despite their ship being possibly the most powerful in the federation fleet, are hailed by Shinzon's Viceroy Vkruk (Ron Perlman) and given transport co-ordinates. Picard, Riker, Troy, Worf and Data transport to Shinzon's location where the New Praetor is revealed to be human, striking similar to a young Picard. After acting particularly strangely towards Diana, never having seen a human woman before, and giving the away team a knife covered in his own blood, the crew return to the Enterprise, where it is confirmed that Shinzon is in fact a clone of Picard.

Question: What is the prototype called?
Answer: B4