The singular for someone who's part of the Royal Engineers (RE), otherwise known generally as a 'Sapper' or if you've worked with them, 'cunt'.
Specialising in all manner of tricksy and dangerous tasks such as IED prodder, wonky bridge builder, FOB construction that'd make a Blue Peter spaceship look like NASA technology and other such mundane tasks that real soldiers can't be bothered doing, they are in fairness, a good bunch of guys to have attached to you on tour.
Their number one task upon arrival at any new and previously untainted area is to blast a suitably sized crater in which to build a bar.
I shit you not, it doesn't matter where you go in the world - if it is or has ever been, a British Army training area, there will be a bar somewhere in it, built by Sappers. We once found one in Belize literally in the middle of no-where. It even had a ground sprung hot tub.
The RE do have one of the shittiest jobs ever, which is the role of Bomb Disposal. Both abroad and homeland UK, the 33 Engr Regt (EOD) are the ones who'll stick on that big funky green suit and go deal with whatever threat has been identified. In order to land yourself this plum number, they have to complete one of the most intensive and demanding courses in the British army.
If you've ever watched Whoops Apocalypse and the EOD scene in the museum, you'll have an idea of what they do with that training...