In the game Half-Life, which enemy is showcased as the final boss?

In the game Half-Life, the enemy showcased as the final boss is the Nihilanth. The Nihilanth is a powerful alien creature and the leader of the Xen forces. It is located in Xen, which is a border world between different dimensions. The reason the Nihilanth is considered the final boss is because it serves as the main antagonist throughout the game's storyline. It controls the alien creatures that have been invading and threatening Earth. The player, as the protagonist Gordon Freeman, has to fight through various levels and enemies to reach the Nihilanth and ultimately defeat it. Additionally, the Nihilanth's defeat marks a major turning point in the game's plot. Killing the Nihilanth severs the connection between Earth and Xen, stopping the alien invasion and resolving the game's conflict. Therefore, it is considered the significant final obstacle that players must overcome to complete the game's narrative arc.