Conversation so far:
What is the etymology of vlachs?
The word Vlach/Wallachian is etymologically derived from the ethnonym of a Celtic tribe, adopted into Proto-Germanic
Why were the Vlachs considered strangers?
Via both Germanic and Latin, the term started to signify stranger, foreigner.
Was the term Vlachs considered derogatory?
The term was also used derogatively for non-Romance-speaking peoples, in recent times in the western Balkans.
Was the term Vlachs ever not used in a derogatory way?
Yes, the term eventually took on the meaning of shepherd, nomad.
Is there anything else interesting about the etymology of the word Vlachs beside the etymology and meaning?
Nowadays, the term Vlachs is used in scholarship for the Romance-speaking communities in the Balkans, especially those in Greece, Albania and North Macedonia.

Question: Who first coined the term?
Self-contained rewrite: Who first coined the term Vlachs?