Earthshaker

Introduction
Disclaimer: This paragraph isn't plain fact, it's displaying an opinion which may, by definition, be wrong.

Although Earthshaker is a Strength-type hero, it's likely you won't be able to hit your enemies by auto-attacking ; his signature skill, Fissure, requires a rigorous positionning, most often far from enemy heroes, especially early and mid-game. Indeed, a good positionning, timing as well as being able to react quickly to an eventual positionning mistakes from your opponents may you give opportunities to block, or, at least, to slow his escape, giving a sure kill and thus give an edge to your team.

Nonetheless, due to his positionning constraints, Earthshaker won't get the chance to kill creeps early on ; as a result, he is mostly played as a support. Further more, he is a strong ganker early and mid-game, still thanks to his Fissure, and therefore won't have much time to farm.

Though, his other skills require him to be close to enemy heroes, because they deal AOE damage (and stun). Thus, he must be able to be quickly in the center of the action, especially for his ultimate skill, which deal more damage the more enemies (heroes or creeps) are hit. As a consequence, Blink Dagger is the most common item choice on this hero.

Unlike popular belief, his main purpose, in teamfights, is not to initiate, or should not be. Before a teamfight begins, the opposing heroes will probably be wisely spread, to avoid having too much people getting hit by Earthshaker. Nevertheless, if the teamfight has already begun, due to someone else initiating, it's more likely they will do positionning mistakes which may lead Earthshaker to catch more heroes when jumping in. Further more, your team will benefit more from your stuns if they are already in position.