Step 1: Conceptualization:
The query requires identification of the progenitor of the Indian Society of Oriental Art, a pivotal entity linked to the Bengal School of Art.
Step 2: Elaboration:
The Indian Society of Oriental Art was established in Calcutta (present-day Kolkata) in 1907. Its establishment was initiated by a collective of artists and European art patrons aiming to foster and advance a contemporary art movement rooted in indigenous Indian artistic traditions, diverging from British-promoted styles. Although his brother Gaganendranath Tagore was instrumental as a co-founder and administrator, Abanindranath Tagore served as the principal artist, educator, and conceptual leader of the broader movement the society was formed to champion. He is broadly recognized as the progenitor of the Bengal School, with his artistic vision propelling the society's inception. Consequently, within the artistic movement's framework, Abanindranath is deemed the foremost founding individual. E.B. Havell was a British advocate and theorist who partnered with Tagore, while Rabindranath Tagore did not directly participate in the society's establishment.
Step 3: Conclusion:
Abanindranath Tagore was the principal figure and founder of the Indian Society of Oriental Art.