[quote=1Charak2]
when was the first ”roshan” born/created
[/quote]

The First Roshan was born circa 130 B.C.E.
He comes after Legion's time, but has been technically dead for far longer as I believe Legion possessed Cain far earlier before Roshan gained his current body.
The Second Roshan assumed the name (and started the tradition) about 5 years after the First's Death, though he was killed by the Third.
The Third is still technically alive, a Living Husk of an Immortal.
The Fourth was killed by the First/Sixth and memories absorbed (but in his wisdom, the Fourth did make a back-up homunculus and is actually alive but inactive.)
The Fifth was killed by the First/Sixth and memories absorbed (he had no back-up plan for his death.)
The Sixth is the First.