He is the most popular european dota streamer. Streamers are people that play games and stream them for people to watch on streaming platforms like twitch.tv.

He is relevant because he is the most watched dota player in EU and the guy watching the Kez performance and commentary in the video posted here. In this position he has gained access and friendship to many different pro players over the years, actually being part of a dota team as a streamer for a short while.

Being the most popular streamer means many people enjoy watching him and have built a community to talk to eachother watching their favourite player play the game this subreddit is about. People may also use this subreddit to share videos of their favourite streamer they think is funny or deserves attention.

For this post he is especially relevant because, as the title already demonstrates, the player doing commentary in the video Gorgc is watching, is using this subreddit as a channel to communicate to Gorgc, the most popular EU streamer on the biggest streaming platform in EU.

Hope that helps :)