Lucifer, also known as Satan, is a figure prominently featured in various religious and cultural narratives. However, the concept of "closest friend" is not explicitly defined in these narratives. Therefore, it is difficult to definitively answer this question.
The Bible, primarily in the Book of Isaiah, portrays Lucifer as a powerful angel who fell from grace due to pride and ambition. This portrayal doesn't focus on personal relationships or friendships.
In other interpretations, Lucifer is sometimes presented as a rebellious figure who challenged God's authority. This interpretation might suggest a sense of camaraderie among those who joined his rebellion.
Ultimately, the concept of Lucifer's "closest friend" is a matter of interpretation and speculation. There is no definitive answer based on established religious or cultural texts.