Final answer:
The enzyme used to create cDNA from mRNA is reverse transcriptase, which is utilized both by retroviruses and in molecular biology research.
Step-by-step explanation:
The enzyme used to make cDNA, which is an intron-free DNA copy of mRNA, is reverse transcriptase. This enzyme uses RNA as a template to synthesize DNA, a process that is essential not only in nature, particularly within retroviruses like HIV, but also a key tool in molecular biology laboratories. The creation of cDNA allows for the study of gene expression without intronic sequences and is crucial for various applications like cloning, sequencing, and gene expression analysis.