Neon Genesis Evangelion Is rei some sory of alien?

Where in the hell did you get that idea?

They created Rei for the purpose of instrumentality, but gendo had his own agenda's seperate from SEELE so didnt inform them that Rei was a clone consisting of Yui & Lilith(First angel) SEELE attempted to do roughly the same with Kauro... i think, that bit is uncertain. As for Instrumentality... it was to merge all life with all there faults into one being that would be theoretically perfect & at peace

 

But they did eventually want to create thier own angels. That was one of thier 'secret purposes'. It goes with teh whoel playing god thing.