dynein

A motor protein found in cells. Other examples of motor proteins are actin and kinesin. Dynein interacts with microtubules, pulling its cargo along the length of the tubule, unless it is anchored. This is the case in cilia and flagella; the microtubule and the dynein's cargo are anchored together, so they bend instead of moving, and this allows the cell they're attached to to move.

Dyneins are a group of motor proteins which, unlike most other known motor proteins, actually move toward the (-) end of intermediate filaments (which are polar). They are exceptionally large proteins (roughly 1000 kDa). The have two heavy chains and various intermediate and light chains.

Dyneins generally considered either cytosolic (they move vesicles and kinetochores around in the cytoplasm) or axonemal (these are the kind that make flagella, like the tail of sperm, and cilia, like those found in the airways of humans (which help sweep out mucus and other junk from the lungs, but do not survive in smokers, which is why smokers sometimes cough up big plugs of mucus), move).
Other motor proteins familys include Kinesins (which also move on intermediate filaments) and Myosins (which move on microfilaments).