Who owns the most number of subscribers on YouTube?

 As of my knowledge cut-off date of September 2021.

The YouTuber with the most subscribers was T-Series, an Indian music video channel. At that time, T-Series had over 190 million subscribers, making it the most subscribed YouTube channel in the world.

However, please note that subscriber counts are always changing, so the current most subscribed channel may be different at the time you're reading this.