Mr Groff is played by Alistair Petrie
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Netflix's Sex Education: Meet the cast

15. Mr Groff is played by Alistair Petrie
Adam's dad and Principal of Moordale High is played by English actor Alistair Petrie. Alistair has starred in several productions including ’Sherlock’, ‘The Night Manager’, ‘Vera’ and ‘Deep State’. More recently, he appeared in 2019’s ‘Hellboy’ alongside David Harbour as Lord Adam Glaren and in ‘Rogue One’ as General Draven. [Netflix]