crept

before 900; Middle English crepen, Old English crēopan; cognate with Dutch kruipen, Old Norse krjūpa

1. See crawl¹.

The verb creep comes from Old English crēopan, a strong verb (that is, a verb from a root that has vowel changes in its inflectional forms, as sing, sang, sung ).
The four principal parts of crēopan are crēopan (present infinitive and the dictionary headword), crēap (past tense singular), crupon (past tense plural), and cropen (past participle). The verb has very many bewildering dialect forms, variants, and spellings in Old English and later in Middle English.
Around 1300 we see the first appearance of inflections of weak verbs (also called regular verbs, with no vowel changes), like love, loved, loved, initially in the past tense. William Tyndale’s translation of the Bible (1534) has the past participle crept, replacing the strong form cropen. Some descendants of the Old English strong verb lived on in certain British and American dialects, such as the past tense crope, which shows up in the speech of runaway slave Jim in Mark Twain’s The Adventures of Huckleberry Finn (1884): “I crope out, all a-tremblin’.”
The slang meaning of the noun “an obnoxious, disturbingly eccentric person” arose in the late 19th century, connected with the now obsolete meaning “a person who creeps along; a sneak.”