BT-1 assassin droid

"All this effort for a simple astromech?" "Not exactly. This is BT-1, a "Blastomech" prototype. Does enough to pass as an astro, but it's primarily a cover. It's a specialized assassin droid."

- Darth Vader and Chelli Lona Aphra talking about BT-1.

BT-1 assassin droids, also known as Blastomechs, were a type of assassin droid that were designed to look like ordinary astromech droids.