A Soong-type android is an artificial life form first developed by Dr. Noonien Soong. They are distinct from other androids by virtue of their positronic brains, which are considered complex enough to permit the rise of sentient thought.
Soong's first prototype android was named B-4.
Soong secretly built an even more advanced android, giving it both the form and the memories of his wife, Juliana Tainer.
Data was able to partially duplicate Soong's work by creating an android daughter named Lal.
Others attempted to duplicate Soong's work, including Dr. Bruce Maddox and Lars Patek.