Step 1: Read the question.
We must name the founder of the Indian Reform Association in 1870.
Step 2: Place the body in context.
It was a Bengal Renaissance reform organisation tied to the Brahmo Samaj movement, focused on women's education, temperance, and cheap literature.
Step 3: Recall the founder.
After returning from England in 1870, Keshab Chandra Sen set up this association to carry reform ideas into practical social work.
Step 4: Rule out Raja Ram Mohan Roy.
He founded the Brahmo Samaj in 1828, decades earlier, and was not connected to this 1870 body.
Step 5: Rule out the remaining names.
Devendranath Tagore led the Brahmo Samaj but did not found this association, and Ishwar Chandra Vidyasagar is linked to widow remarriage and education reform, not this institution.
Step 6: State the answer.
The founder was Keshab Chandra Sen, option C.
\[ \boxed{\text{Keshab Chandra Sen}} \]