In the novel Frankenstein, Victor and Henry are lifelong friends who appreciate each other very much. Henry basically grew up in the Frankenstein estate and he was very much treated as a part of Victor's family.
Victor and Henry separated when Henry left for Ingolstadt. However, he met Victor again when the latter was suffering from what is known in the story as "insane fevers", or fits of anxiety that Victor suffered after creating the creature.
Since Victor and Henry spent so much of their childhood together, their environment made it possible for them to develop similar characteristics. Hence, Henry possessed the same great qualities that made Victor successful, such as the passion for learning, the ambition to reach new goals, the dedication to his field of work, and the ability to challenge himself. These characteristics were all part of Victor's own personality prior to the creation of the monster.
What made Victor and Henry very different was that Henry did not allow ambition to turn into an obsession, nor did he intend to become anything but a very well-educated linguist and philosopher. Contrastingly, Victor's ambition did become an obsession that tainted his soul, his mind, and his heart altogether. Hence, Henry represents Victor's former self before ambition ruined his life forever.