Similarities between Vedic literature, Hinduism and Cuture were noted by  Sir William Jones in 1786.

Lord Rama.

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A treaty signed by the Hittites and Mitannis dating to the fourteenth century BC calls upon Indara/Indra, Mitras(il)/Mitra, Nasatianna/Nasatya and Uruvanass(il)/Varuna, all known to Rig-Veda and Avesta.

There were similarities in rituals too. In India, upanayana is a ritual by which a boy becomes a full member of his class. Zoroastrians have a similar ceremony called Navjot which is still practiced by Parsis. The Rig-Veda refers to the drink soma which was drunk at sacrifices and  which caused invigorating effects. The Avesta gives physical descriptions of the plant haoma which causes similar effects, though the plant identified as haoma by modern Parsis is a bitter herb which does not get your drunk, but just bitter.

Even though there are similar words like haoma (soma), daha(dasa), hepta (sapta), hindu (sindhu), and Ahura (Asura