Actually, Hinduism started out as a purely Aryanic religion (the Gods of the Vedas are similar to the Gods of the Hittites and the Nordic gods and the Irani pre-Avestani gods) with their two families of gods: Ahuras/Asuras/Aesir and Devas/Daevas/Vanir. Then it merged with Dravidian religions and you got Shiva and Vishnu and then it added on various ideas from Greeks and also from local kings and queens who fought against the invasions of the Greeks, Kushans, White Huns, Scyths etc. (the goddess Devi for example)
The Vedas are the original source teaching of the Hindu tradition from which its many branches of Vedanta, Yoga and Tantra have emerged. They are also the background from which Buddhism evolved. They are the oldest known Indo-European religious tradition and pre-date the Greeks by several centuries.
They began in the civilization of the Indus Valley culture, and as they speak of Sarasvati River going from the mountains to the sea, this dates the Vedas well before 2000 BC, contemporary with the pyramids of Egypt.
The Vedas are said to be a manisfestation of Sanatana Dharma, which literally means the eternal truth. This is the oldest literature of the Indian people.