excogitatorn.

/ɛksˈkɒdʒɪteɪtə/Etymology: agent-noun < Latin excōgitāre: see excogitate v. and -or suffix.
the mind > mental capacity > thought > [noun] > thinking out > one who thinks out
1847 W. Hamilton 28 An original excogitator of the doctrine.
This entry has not yet been fully updated (first published 1894; most recently modified version published online March 2018).