C16: probably related to Old English dol stupid; see dull
Word Origin and History for dolt
n.
1540s, perhaps a variant of dold "dull, foolish," influenced by dulte, dolte, past participle forms of Middle English dullen "to dull, make or become dazed or stupid" (see dull (adj.)). Related: Doltish; doltishly; doltishness.