Which country is the best friend of Saudi Arabia?

Could you please enlighten me on the topic of Saudi Arabia's diplomatic relations? I'm particularly interested in knowing, which country stands out as Saudi Arabia's closest ally or best friend? Given the region's complex political landscape, I'm curious to understand the factors that contribute to such a designation. Is it based on economic ties, military cooperation, or perhaps cultural affinities? I'm looking for a concise yet informative answer that helps me grasp the essence of this relationship. Thank you in advance for your assistance.