Any ideas on the font used in this famous logo? Thanks in advance!

Franklin Gothic Heavy  Suggested by jum 
ATF Franklin Gothic Black  Suggested by jum 
Frint Heavy  Suggested by bs00th 
Plymouth Serial  Suggested by Meco01 
RUN ET-C  Suggested by flourishprosper 
Arial Black  Suggested by jum 

I have now found out what this font is, it's FRINT HEAVY, but a free alternative is FRANKLIN GOTHIC HEAVY. Hope this helps!

In the original, hate to say this but i believe it’s Arial Black http://www.logoeps.com/run-dmc-logo-vector-eps-ai-cdr-free-download/7593/#download-link

Actually, this is incorrect. Your reference logo is not the original, it's a recreation someone who is not detail-oriented made. If you look up run DMC images you can see clearly that the letterform of the R itself is drastically different in original source material as compared to the vector file you linked.

Noticed that R, anyways it would be nice if you came up with a link to the correct Logo, there are quite a few versions around.
In fact RUN DMC themselves are not really sure about what font they like to use on their album covers: http://bit.ly/24pGW1O
Secondly a suggestion what font it would be in your opinion would also answer the question a bit further.

I created this do it yourself Run DMC kit. It contains a bunch of SVG files as well as outlined font png files for use in many craft maker machines and projects. Mainly the cricut and silhouette machines. It's like a build your own RUN DMC logo kit.

Anyone know where I could fint the FRINT HEAVY font or the whole family - to buy or download? Thanks!

You're looking for this font: https://www.fonts.com/font/itc/itc-franklin-gothic-lt/heavy

I have that one, but it's not that. And @bs00th said the font is FRINT HEAVY.

I don’t think that’s feint heavy, it must be a stylized version of Franklin Gothic. (Not Franklin Gothic Heavy)

ATF Franklin Gothic Black gives a very good result on the topmost RUN DMC image
and Plymouth Serial Black is also pretty close.

That one is close, but the C doesn’t match.