Every piece in chess is unique:
Pawns: Can transform
Knights: Only animal in the game
Rook: Only non living piece
Queen: Ehh...
King: Only piece you can't capture
Bishop: Only Religious Piece
Therefore, the queen is the most unique cause it's the only one that's not unique
The pawn is also unique in that it is the only piece that doesn't capture the way it moves.
As tuna mentioned, the knight is not an animal even though the piece resembles a horse's head.
However, if you consider the knight an animal, then it's a dead animal - and the rook is not the only non-living piece.
The queen is unique because it is the only piece that can do everything that at least one other piece can do (in fact, three other pieces).
By the way, unique is an absolute and should not be modified.
^^^^ Like Ganesha you mean?