Kotei Emperor of The Empire (Male)
Makoto Naegi (Male)
Top of Brains is between Luke, Len, Killua, Schrodinger, Huey, Shiota, Ciel, Tanya, Rimuru, Pride, and possibly Vivi, although Alladdin is thought to also have access to Rukh of all things good so it's possible is very intelligent too, also Mare Bello Fiore is known to study excessively although we have no idea what or how he learned his stuff before he became powerful. His memories were artificially generated after all, for all we know Mare could be tapping into astrophysics and quantum tunneling when he casts spells. Also Schrodinger is technically The Doctors "Son" so he must know alot of surface knowledge and who knows what kind of IQ is lurking beneath something that can quantum tunnel through reality). Rokkuman Mega Man also is a robot and might be able to tap into advanced hacking skill.
The most potentially intelligent is Schrodinger.
The most intelligent known is Pride as all Homonculi carry knowledge of The Gate and thus an entire universes knowledge.