There are certainly some people whose personalities allow them to get in front of a crowd with little fear and project their voice.
But, of course, being a great public speaker requires much more than a strong will and loud voice. Like any other skill, the only way to look like a true "natural" on stage is through disciplined practice.
And don't feel that anything you may consider a negative trait — a speech impediment, heavy accent, social anxiety — needs to hold you back. For example, this year's Toastmasters International World Champion of Public Speaking, Mohammed Qahtani, has dealt with a stutter for his entire life, and learned to keep it from emerging in his speeches.
And even if it did pop up, he wouldn't be worried. He told Business Insider that he knew some of his competitors had a stronger voice or more impressive stage presence than he did, but his gift was comedic timing. Everyone has their strengths, and they can compensate for your weaknesses.