The Saboteur first made an appearance during the Greenborough missions, added in 1.3 Patch. He is like any other named NPC, joining the player's force for only certain missions, yet starts at Rank 1 and gains . (Note that earned with the NPC does not carry over to the Barracks' unit because both are considered different types of units).
For a short period of time (6/8/2012-6/11/2012), the Saboteur was available for training at the Barracks, for 55 . As of the 2.1 Patch, the Saboteur was permanently added to the Barracks, albeit for 65 .
The Saboteur is very similar to the Demolitionist, except the Demolition Charge can do some major damage, although with a lengthier cooldown compared to that of the Demolitionist's zero cooldown, also the Demolitionist is indirect targeting, while the saboteur is contact (backstab). Another advantage is that the Saboteur can be upgraded with a pistol attack at rank 2, allowing some rather weak anti-infantry capabilities. (The NPC version unlocks the pistol at rank 1)
The Saboteur excels at destroying vehicles, especially support vehicles, mainly due to the massive amounts of damage delivered in Demolitions Charge. Compared to the Demolitionist, a premium is being paid for the increased damage and being available at a much earlier level. While the latter has more charges and reduced cooldown, the player isn't using extra turns to deliver that damage. With increased ranks, the Saboteur can tear down a Peacemaker into pieces with a single attack.
At later levels, the Saboteur is rendered obsolete by the availability of another premium unit, the Guerrilla, and it is questionable if this unit is worth the price tag.