This house was built in the 1950s. The wood is tongue and groove (thank you @Ecnerwal) and appears to be the only wall material--there is no drywall under it. I can tell because some of the knots of the wood have fallen out and I can see inside to the space where the electric and plumbing travel through the house.
It currently looks worn and I want to know if there is a way to repair it. Or if I cover it up, is there a way to do it with minimal damage, so some future house owner can restore the original walls?