c. 1300, obligen, "to bind by oath, put under moral or legal obligation, devote," from Old French obligier "engage one's faith, commit (oneself), pledge" (13c.), from Latin obligare "to bind, bind up, bandage," figuratively "put under obligation," from ob "to" (see ob-) + ligare "to bind," from PIE root *leig- "to tie, bind." Main modern meaning "to make (someone) indebted by conferring a benefit or kindness" is from 1560s.
<a href="https://www.etymonline.com/word/obligor">Etymology of obligor by etymonline</a>
Harper, D. (n.d.). Etymology of obligor. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/obligor