R6-S1 was the astromech unit of elite Bothan pilot Eelo Begraas. Nicknamed "Shootfirst", the droid helped him fly his customized Z-95 Headhunter Dicer.
Behind the scenes
This droid was twice referred to as R6-S1 and once referred as R6-A1.
Sources
Troop Movements on Wizards.com (original site is defunct) (First mentioned)