We are asked to find:
\[
\tan^{-1} (-\sqrt{3})
\]
We know that:
\[
\tan \frac{\pi}{3} = \sqrt{3}
\]
Since the argument is negative, we are looking for the angle in the fourth quadrant. The value of \( \tan^{-1} (-\sqrt{3}) \) is:
\[
-\frac{\pi}{3}
\]
Thus, the correct answer is \( -\frac{\pi}{3} \).