A rectangle, derived from the word "rectum," is a two dimensional shape. However, unlike all other two dimensional shapes, all rectangles of all sizes can be fitted snug into the rectum, whether it's the whole rectangle or just a corner. The rectum will repel against all other two dimensional shapes because of complications involving electromagnetism. The cirtangle is considered the three dimensional counterpart of the rectangle.
The rectangle's common enemy is the eclpictic circle. Millions of innocent shapes were made extict during their wars, including the smircle and the dodecadiahepticlon. However the true ARCH NEMESIS of the Rectangle (and all his known comrades and grandparents)is the Oblong, the almighty, anti-rectum evil doer whose super-powers include laying radioactive eggs and destroying a soufflé from 300 yards using only his left testicle.