B-4

One of three failed prototypes built before Lore & Data
Physically identical to Data & Lore but had a much less advanced positronic brain;
Had difficulty understanding simple concepts and learning new information
2379: Discovered by the crew of the USS Enterprise-E on Kolarus III, parts had been planted there by Shinzon
Reassembled by the Enterprise crew but had no memory of his past
Data transferred his memories into B-4 hoping it would help him develop, could not fully process or remember the memories
2390s: Had been disassembled and stored at the Daystrom Institute
After the synthetic ban ended, Altan Soong used parts of B-4, Data, Lore, and Lal to build a hybrid android