Design wise, he's based off a Triceratops and like Flame Mammoth from the original Mega Man X, he is a large Reploid based on a large extinct animal, with mastery of an element (water, though Flame Mammoth's is fire), a penchant for cruelty, and extreme pride in his size and power, an arrogance which leads to his downfall.
During the Rebellion forces' reign, Silver Horn was a cruel tyrant who tortured and destroyed many captured Reploids who refused to join the Rebellion forces, even the original Steel Massimo. He also held Nana captive and coerced her to function as the Tianna Camp's systems operator, or else he would have the remaining prisoners held there executed. He also enjoyed mocking those he considers weak, including the original Steel Massimo, as he laughed in the new Massimo's face as he described his torture.
Stats and Abilities
In battle, the three horns atop his shell serve as the projector of his deadly water-based "Pressure Abyss" attack. He can also sheathe himself in a liquid metal coating, increasing his defense greatly.
Silver Horn had the temporary name "Trine Canonhorn" (トライン・カノンホーン,"Trine Canonhorn"?) during his development, and a Mechaniloid similar to him, Twin Barrel (ツインバレル,Twin Barrel?), was planned to appear in the latter half of the game.
Given his size, it's easy to assume Silver Horn may have once occupied a position as a construction worker or similar profession, moving or destroying large rocks. This assumption is aided by the fact that he is equipped with large high pressure water cannons, similar to a sand blaster or water jet cutter.