What was the name of the character who could communicate with the dead?

The Lost character who could communicate with the dead was Miles Straume.

Miles, played by Ken Leung, was introduced in season four as a member of the freighter team aboard the Kahana. He worked as a medium, claiming to hear the thoughts and voices of deceased people. His ability made him valuable to Charles Widmore, who believed Miles could interrogate the dead and obtain information about Ben Linus.

Miles's power was revealed to have begun during childhood. He could sense or hear the thoughts of the deceased, and he eventually turned that ability into a profession. His sarcastic, distrustful personality initially put him at odds with the Oceanic Flight 815 survivors, but he gradually became an ally.

The character also has an important connection to the island's history: Miles is the son of Dharma Initiative scientist Pierre Chang. He later travels through time with the survivors and works with the Dharma Initiative in 1977. His name was reportedly chosen because it resembles “maelstrom,” meaning a powerful whirlpool.