Final answer:
Laocoon, a Trojan priest of Poseidon, warned the Trojans against accepting the wooden horse left by the Greeks, saying "Beware of Greeks bearing gifts." However, he was silenced by two sea serpents sent by Athena or Poseidon, allowing the Trojans to bring the horse inside Troy.
Step-by-step explanation:
The individual who attempted to stop the Trojans from bringing the horse inside the gates was Laocoon, a Trojan priest of Poseidon. Laocoon famously warned the Trojans of potential Greek deceit with the phrase "Beware of Greeks bearing gifts," about the large wooden horse the Greeks left outside the city of Troy.
Despite Laocoon's warning, the deities Athena or Poseidon, depending on the version of the myth, sent two sea serpents to silence him and his sons, effectively preventing his counsel from influencing the Trojans' decision to bring the Trojan Horse into their city, which ultimately led to their downfall.