What is the name of the creature that attacks the Fellowship at the West-gate of Moria?

The creature that attacks the Fellowship at Moria’s West-gate is the Watcher in the Water. It lurks in the dark pool beside the Doors of Durin, the western entrance to the ancient Dwarven realm of Moria.

In The Fellowship of the Ring, the creature seizes Frodo with a long, pale-green, luminous tentacle as the Company tries to enter Moria. The others rescue him, but the Watcher then attacks the gate and forces the Fellowship to retreat inside. Once they are through, it seals the entrance behind them, leaving the Company trapped in Moria.

Tolkien never explains exactly what the Watcher is or where it came from. The text describes many tentacles but does not give it a species, which is why readers sometimes compare it with a kraken or other legendary sea monsters. Gandalf suggests that it may have been driven out of deeper places beneath the mountains.

It is often confused with the Balrog, but the Balrog appears much later, deep inside Moria. Shelob is another separate creature, encountered near Cirith Ungol.