What is Gulliver's primary occupation before arriving in Lilliput?

Gulliver's primary occupation before arriving in Lilliput is that of a sailor. This is evident as he has embarked on several voyages, which is a central aspect of his life before the events of the story. His experiences at sea are integral to the narrative as they set the stage for his adventures and encounters with different cultures, including the tiny inhabitants of Lilliput. His profession allows him to navigate the world, leading him to unusual lands and situations, which is a hallmark of the tale. The other options do not align with Gulliver's character as depicted in the story; he does not engage in medicine, law, or military service. Instead, his life as a sailor provides the necessary context for his travels and the various encounters that unfold in the narrative.