The formless photonic beings of the world Kasq, descendants of holograms who outlived their organic masters, who spent two centuries building the cadet SAM as their emissary to organic society.
The Makers are the Kasqians responsible for SAM, the photonic cadet of Starfleet Academy. Their ancestors were holograms built to serve organic beings. When those masters died out they withdrew to Kasq, a world where time runs far faster than outside, and came to exist largely as non-corporeal holographic energy.
SAM was their experiment in rejoining the wider galaxy, some two hundred years in the making. After she is badly damaged during the events of Come, Let's Away, Chancellor Ake takes her home in The Life of the Stars, where a Maker played by Chiwetel Ejiofor judges her beyond repair and decides to terminate her.
Ake argues that the fault lies in SAM's inability to process trauma. The Makers, who revere the Doctor for his centuries among organics, agree to rebuild her as a child, and the Doctor remains on Kasq for seventeen years to raise her.