Question and Answer

Q. Who is the Founder of Hindu Religion?

A.  Normally a philosopher/prophet comes up with a system revolutionary or at least that did not exist before. Accepting the new system, disciples and other people start following the religious system. And for the new religion that person is the founder.
In case of Hinduism

The system existed from time unmemorable.

1. Hindu scriptures talk about things that happened at periods of time, whose specified count is much much higher than the period well known to history scholars of current time. (yuga, manvantara, kalpa etc.)
2. Even the scientific excavations show the existence of well-developed worship, at very early periods.

There were, of course, very many philosophers who came up with new systems. However given the wide spectrum of Hinduism, its accommodativeness towards new ideas and philosophies and all the new changes, made it a healthy religion that does not get stagnant.

People used their discretion to find the suitable paths through the wisdom of one or more philosophers and there was a real diverse system.
So, there is No Single (Human) Founder for Hinduism and it existed from time unexplored, as a religion.