Tornus was a pony who was born and raised in Ponyville on his parent's side he was a farmer just like his parents when he grew up he was lured away from Ponyville by Queen Chrysalis into Changeling Kingdom where he was transformed into a changeling he hated being one until his Changeling mind took over him and he became a changeling working for her.
He has the same personality as Pharynx
In New Changeling Tornus is first introduced + his backstory
In Twilight Moon part 1 he meets Twilight Sparkle
In Plot is his last appearence in season 1
Tornus was thought to be presumed deceased when Apple Jack offered to help him from falling off a cliff he refused and fell to his presumed demise it is revealed in the first episode of season 2 he is alive similar to Zira's death from the lion king 2 he is voiced by the same voice actor as Pharynx he is also the revealed antagonist turned protagonist.