Vaerin and his trophy were seen on Pendragon in 2003 when the original batch of trophies was tested, but nobody reported them on live servers until patch 1.96c in November 2008.
Vaerin wanders outside the south entrance of Avalon City. He's usually on the ramp but may go a few units past the edge, in which case he's hard to see because of the steep slope.
To make him pop, kill unnamed Drakorans on the ramp. It can take several hours.
Vaerin's trophy is identical to Martley's.
Many thanks to Daxx for information about Vaerin in 2003.