First we should start about the Origin of the Word Khmer and the ancient Kingdom of "Kambuja" today
in Khmer Language "Khampuchea" or just in English Cambodia.
This Kambu or Kampu + Mera (snake lady) story, to all probablity, is only a later time myth invented to give some credible explaination as to the origin of name 'Kambuja' & 'Khmer'.
Sage Swaymbhava Kambu is stated to be a scholar king from North India who visted this region and married a snake lady and set up the Kambuja or Kamboja kingdom.
The name Khmer is claimed to be derived from Kambu +Mera == > Khmer.
And the Kambujas are also supposed to be derived as...Kambu+jas =Kambujas(Jas=descendents) =Desscendents of sage Kambu.
But who was this sage/warrior Indian king Swambhava Kambu????? Is there any legitimate documentation to verify the historicity of this legendary figure of Indian origin.
The scholars say that Indian scholar king Swayambhava Kambu does not exist in any ancient Indian Sanskrit/Pali literary records. They say that this myth of sage king Kambu is just one phantastic explanation offered by later-time brahmanical class of Kambuja to give a legitimacy to name 'Kambuja' and 'Khmer'.
By the way, the Kamboja and Kambuja is also the name of one ancient well known Indian/Iranian ruling tribe located in Pamir/Badakshan (north Afgfhanistan, Tajikstan & north of Kashmir] and they also find very prominent mention in King Ashok'as rock edicts. There other sections are known to have migrated as far as Uttarpardesh, (Bengal/Burma (2nd 3rd AC), Gujarat and Sri Lanka (4/3 c BC). Kamboja and Kambuja, as a tribe and country/kingdom, also find prominent mention in numerous ancient Sanskrit, Pali literature. Numerous historians have also linked these Kambojas/Kambujas with ancient Iranian name Kambysis, which is the name of some famous persian kings of Achamenian dynasty of 6th c BC.