Step 1: Concept
The history of virology began with experiments designed to identify agents smaller than bacteria that could cause disease.
Step 2: Analysis
In the late 19th century, Dmitri Ivanovsky and Martinus Beijerinck studied a disease in tobacco plants that could pass through porcelain filters.
Step 3: Reasoning
Tobacco Mosaic Virus (TMV) was identified as the "contagium vivum fluidum" or infectious living fluid. scientific consensus and historical fact confirm TMV as the first discovered.
Step 4: Conclusion
The first virus discovered was the Tobacco Mosaic Virus (TMV).
Final Answer: (D)