Sméagol’s alter ego in J.R.R. Tolkien’s The Lord of the Rings is Gollum.
Sméagol was a river-dwelling relative of the Hobbits who found the One Ring after his kinsman Déagol discovered it in the Anduin. Sméagol murdered Déagol to obtain the Ring, and its influence gradually transformed him. He became isolated beneath the Misty Mountains, where he was known as Gollum, a name associated with the swallowing sound he repeatedly made.
Tolkien presents Sméagol and Gollum as competing aspects of one damaged character rather than as two entirely separate people. The Ring intensifies his possessiveness and helps extend his life, while long isolation changes his body and habits. Later, Gollum becomes central to Frodo’s journey because he knows the route into Mordor.
Déagol is a frequent wrong answer because he is closely linked to the Ring’s discovery, but he is not Sméagol’s alternate identity. Gríma Wormtongue is a different character from Rohan.