Let \( G = \mathbb{R}^* \times \mathbb{R} \), where \( \mathbb{R} \) is the set of all real numbers and \( \mathbb{R}^* = \mathbb{R} - \{0\} \). Define an operation \( \circ \) on \( G \) as \( (a,b) \circ (c,d) = (ac, bc + d) \). Then, the identity element of the group \( (G, \circ) \) is _____.