plodder

noun3

1. •
   A person who, or animal that, plods.

   • Brown rats, black rats, grey rats, tawny rats, Grave old plodders, gay young friskers […] — 1842
2. •
   A person who works slowly, making a great effort with little result; a person who studies laboriously.

   • Study is like the heaven’s glorious sun That will not be deep-search’d with saucy looks: Small have continual plodders ever won Save base authority from others' books — 1595
3. •
   A machine for extruding soap, margarine, etc. through a die plate so it can be cut into billets.