|He's alongside Nathan in the intro; he also runs into Nathan in the Machine Tower and Chapel Tower; he's later a boss in the Observation Tower
Castlevania: Circle of the Moon
Hugh is the son of Morris Baldwin and, like many others series heroes, a Belmont descendant of a different surname. Because of the strong bond between the Baldwin and Graves families, he and Nathan Graves became great friends during their years of training under the watchful eye of Morris Baldwin.
It was obvious from observing their training that Hugh was superior in terms of skill, and Hugh always showed great pride in that position. However, when his father started to favor Nathan, it was beyond his understanding. "What was it that his father saw?" everyone wondered. Over time, the constant attention paid to Nathan began to make Hugh feel resentful, jealous and eventually hateful. Finally, Hugh was pushed over the edge when Morris, the elder, selected Nathan as the bearer of the Vampire Killer whip and the sub-weapons rather than Hugh, who had proven himself to be more skillful.
When the trio arrived at the castle, a preemptive strike by Dracula landed Hugh and Nathan in the castle's catacombs. Hugh broke free from Nathan, pushing him aside, and set out to look for his master. He was having little to no luck and became bitter when Nathan was able to make better progress. The hate swelled to the point where Hugh's mind became clouded, which made him easy prey for Dracula's dark influence. Nathan learned this all too well when he entered the castle keep only to be attacked by a nearly possessed Hugh, who struck with rage.
Nathan emerged victorious, the blunt force of the battle knocking some sense into the shaken Hugh (or knocking the spell's influence out of him, as it were); Hugh, who had been watching himself externally, helplessly, came to finally understand why his father made the decision to hand down the weapons to Nathan. The humbled Baldwin gave Nathan his blessing to finish the search and bring their master to safety, and he vowed, thereafter, to restart his training with a newfound respect.