The megakaryocyte is the enormous purple-blue cell in this picture. You can actually see its edges fragmenting into platelets, the little bandaids of the bloodstream. When all the cytplasm is bone, the nucleus will be recycled.
A megakaryocyte is often 100 microns across. Although the books remind us that most megakaryocytes reside in the bone marrow, up to 25% live and work in the lungs instead.