The simple and strong Eka has been covered extensively previously, but no tough folder thread complete without it.

Before there were "tactical folders" the Eka with nylon scales was immensely popular in the UK and Europe among military members from the mid-late 1960s (1968 I think), survival courses designed around it, and used hard and heavy to no ill effect. It really introduced the first successful bolted knife, successful even in the USA under the Normark brand with black plastic scales as the Swede and Super Swede, this latest picture version really a Super Swede with blade back not quite so high.

Simple and strong, the tail lock leverage allows an extremely strong lock and the knife gives essentially a folding puukko tough utility/survival knife to the average user, the stainless blade even the same very hard to hurt Sandvik 12C27. Outclassed by the one-handers today, it still is one of the toughest knives in its weight class. Now sadly almost extinct (along with the company) except in one knife of thumbstud pointier design.