First, and understand this Harry because it's very important: Not all wizards are good. Some of them go bad.
11 seconds sound clip from the Harry Potter and the Sorcerer's Stone movie soundboard.
You can hear this line at 00:31:05 in the Blu-ray version of the movie.
Quote context
[...]
- After all, He-Who-Must-Not-Be-Named... did great things. Terrible... yes, but great.
- Harry! Harry! Happy birthday.
- You all right, Harry? You seem very quiet.
- He killed my parents, didn't he? The one who gave me this.
- You know, Hagrid. I know you do.
- A few years ago... there was a one wizard who went as bad as he can go. His name was V...
- No, I can't spell it. All right, Voldemort.
- It was dark times, Harry. Dark times.
- Voldemort started to gather some followers. Brought them over to the Dark Side.
- Anyone that stood up to him ended up dead.
[...]