I think the short answer is: kinda. Mercer was co-CEO, with Peter Brown. He was demoted when his political activities impacted recruitment.
My understanding is that Simons is still holds the majority of RenTec shares, with Mercer around 3rd place. RenTec made Mercer rich, but it is isn't his.
I agree with you. I'm responding to what I think is the spirit of the question. These days if someone is asking about RenTech in the context of Mercer, they're doing so because they're mostly heard about the firm as an auxiliary topic to Mercer's political activity.
And last I was aware, yes, Simons still has the majority of shares. If I recall correctly that's publicly disclosed though.
My understanding is that Simons is still holds the majority of RenTec shares, with Mercer around 3rd place. RenTec made Mercer rich, but it is isn't his.