Paul Heyman is Lesnar’s advocate, and he even shown up to work when Lesnar didn’t in the past few weeks to help work on the storyline leading to SummerSlam. This isn’t anything new for Heyman though because he’s been a backstage advocate for Lesnar for a very long time.
Lesnar’s apparent heel turn on Raw was a pretty selfish and brutal was to go about things. The UFC was explicitly mentioned as well which Dave Meltzer noted on Wrestling Observer Radio was Heyman’s doing.
It was noted that Heyman has been orchestrating much of Brock’s SummerSlam storyline and he did the same thing for his Mania match against Reigns. They want fans to think Lesnar doesn’t deserve the Universal Title so they’ll be happy when someone takes it.
All of this seemed to work very well because they had the crowd chanting “We want Roman” by the end of the show.