The details of this excerpt show that rainsford sees ivan as a(n) individual.

Here is the full excerpt for this question:
Again Rainsford lifted the heavy knocker, and let it fall. The door opened then, opened as suddenly as if it were on a spring, and Rainsford stood blinking in the river of glaring gold light that poured out. The first thing Rainsford's eyes discerned was the largest man Rainsford had ever seen—a gigantic creature, solidly made and black bearded to the waist. In his hand the man held a long-barreled revolver, and he was pointing it straight at Rainsford's heart

from this excerpt, we know that rainsford sees ivan as: alarming

Not only Ivan possesses all the physical feature that really intimidate Rainsford, He also pointed a gun on his chest. This make Rainsford think that ivan is a potential threat for his life, so he feels alarmed at the sight of Ivan