Final answer:
In William Golding's 'Lord of the Flies', Ralph is joined by Jack to explore the island, which marks the start of their important and complex relationship.
Step-by-step explanation:
The character who accompanies Ralph to explore the island is Jack. In William Golding's novel Lord of the Flies, Ralph is elected the leader and decides to explore the island to better understand their situation.
Jack, the leader of the choir boys, volunteers to go with him. It is significant that Ralph chooses Jack, as this decision forms the beginning of the complex and often antagonistic relationship between the two boys, which is a central theme of the novel.