The story
- Old English · inherited fromþæt þū dōn wilt, þæs þe þū wille
- Middle English · inherited fromdo what thou wilt
- English todaydo what you will
From Middle English do what thou wilt, from Old English þæt þū dōn wilt, þæs þe þū wille.
Etymology from Wiktionary, CC BY-SA 4.0.