One of the characters in the Homestar Runner stories and Website.
Strong Sad is, as his name suggests, the brother of Strong Bad and Strong Mad. As his name also suggests, he is angst personified. He doesn't have the evil tendencies of his brothers, however; apparently they disowned him some time ago because he wouldn't help them cheat. He still lives with them, however, though he is more of a friend to the rest of the Homestar Runner gang than to those two. He occasionally helps his brothers out; when this happens, Strong Bad behaves as if he and Strong Sad were on good terms, though such incidents don't usually last very long.
Appearance-wise, Strong Sad is an odd combination. Drawn completely in shades of grey, he is quite obese and actually has the feet of an elephant, complete with massive toenails but no apparent toes. His most distinctive feature, however, is his head, a simple black-and-white doodle which looks suspiciously like the cute blob-thing from Zoloft's advertising.
In the Kick the Can timeline, Strong Sad's counterpart is Sickly Sam, whom The Homestar Runner and Old-Timey Marzipan consider their "worst friend". Whereas Strong Sad is obese, Sickly Sam is emaciated; in fact, his elephant feet are replaced with skeletal feet. Most of the rest of his body is hidden by the burlap sack he wears. His head's shape changes, with the small tail which causes it to resemble the Zoloft blob instead swept up and curled. In addition, his eyes appear to actually be empty sockets. Sickly Sam is just as depressed as his modern version, but perhaps more depressing. Also, the Kick the Can cast seems to be more intolerant of him; whereas the modern cast will usually tolerate his presence, the Kick the Can cast actively expresses that they would prefer he leave them alone.
Strong Sad does not yet appear to have a counterpart in the Stinko Man 20X6 timeline.