The transforming principle was discovered by Frederick Griffith in 1928. However, its identification as DNA was made by Oswald Avery and his team in 1944.
Step 1: Historical background. The concept of the "transforming principle" was first proposed by Frederick Griffith in 1928 during his experiments on \textit{Streptococcus pneumoniae}. He demonstrated that genetic material from heat-killed virulent bacteria could transform non-virulent bacteria into virulent ones. Step 2: Role of other scientists.
Oswald Avery: Later identified the transforming principle as DNA in 1944 through experiments with Avery, MacLeod, and McCarty. James Watson: Contributed to the discovery of the structure of DNA alongside Francis Crick. Rosalind Franklin: Provided critical X-ray diffraction data that aided in understanding the structure of DNA.
Step 3: Conclusion. Frederick Griffith was the first to propose and demonstrate the existence of a transforming principle, though its identity as DNA was confirmed later by Avery and his colleagues. The correct answer is: Frederick Griffith.
