Final answer:
A transcriptional regulator that activates the expression of other transcriptional regulators for inducing a particular cell type or organ is known as a master regulator.
Step-by-step explanation:
A transcriptional regulator that activates expression of additional transcriptional regulators which induce the production of a particular cell type or organ is called a master regulator. These master regulators are central in the hierarchy of gene regulation and play a crucial role in the processes of cell differentiation and organ development. They have the ability to control the expression of many other genes, including other transcription factors, establishing the complex regulatory networks necessary for the development of specific cell types and organs in multicellular organisms.