when was it first written down?
Between 1500 BCE and 1200 BCE
Sanskrit
 Rig Veda, a collection of 1,028 hymns composed between 1500 BCE and 1200 BCE 
who is believed to be the originator of yoga Ancient India traditionally, what is the primary aim of this exercise? The ultimate goal of Yoga is "Moksha" (liberation), although the exact form this takes depends on the philosophical or theological system with which it is conjugated. can you name some texts that expound this in the classical period? Rig Veda,  Upanishad which language was the former composed in? Sanskrit
wiki:19674309
Sanskrit [SEP] Introduction
As a result, Sanskrit had a lasting impact on the languages of South Asia, Southeast Asia and East Asia, especially in their formal and learned vocabularies. Sanskrit generally connotes several Old Indo-Aryan varieties. The most archaic of these is Vedic Sanskrit found in the Rig Veda, a collection of 1,028 hymns composed between 1500 BCE and 1200 BCE by Indo-Aryan tribes migrating east from what today is Afghanistan across northern Pakistan and into northern India. Vedic Sanskrit interacted with the preexisting ancient languages of the subcontinent, absorbing names of newly encountered plants and animals; in addition, the ancient Dravidian languages influenced Sanskrit's phonology and syntax.