Hinduism is the oldest of all religions. Since it was not propounded by an individual, it is the aggregation of the dharmic thoughts of many sages / Rushies. So who has contributed to these thoughts for the first time cannot be clearly declared. If at all one venture to say that it is Veda Vyasa, Vasishta…or Agastya, we cannot say with a proof, who has contributed for the first time for this bunch of thoughts of Hindu dharma. Interestingly, our Rushies, who wrote Vedas, Upanishads, itihasaas, puraanas, upavedas, were focusing mainly in conveying the subject / knowledge / message /… they never tried to focus WHEN they lived and when did they write/ gave / taught these messages.
The historical facts were not crucial for learning the absolute knowledge of life. That may be the reason why they focused only on the knowledge even without mentioning their names, in any place. (However for the astronomy / mathematics / chemistry books written for the last 2,000 years the authors have clearly mentioned the date of composing, their date or the date of birth of their teachers because those data are important)
WESTERN APPROACH VIEWSON THE DATE OF VEDAS. One should very clearly understand that the western scientists, historians, archaeologists will never give the credit of Indian culture beyond 2500 BC, mainly because according to Bible, the God created Adam and Eve on 12th October, 4.00 pm on 4012 BC (or so). So according to their calculation human beings cannot exist before that. Based on this biased / false/ non scientific notion they calculated the historical facts on Hindu culture.
They also had a European superiority complex which prevented them to give credit to Indian culture (as the most ancient). They wanted and always tried (even now) to project Greek, Mesopotamia, Babylonia, and so on as the oldest. However after 1947, many great Indian and foreign unbiased scholars have proven that the first artifact of human made copper and copper items could be excavated from Kalibangan, Bhagavan pura and so on from 8275 +/- 100 BC. Perhaps we can say the archaeological evidence of Indian culture starts from this point, even though Dayananda Sarasathy, Balagangadhara Tilak, and many great Indian scholars and few western scholars have put the period from 10,000 to 50,000 yrs.