[9][non-primary source needed] He grew up on the Lower East Side of Manhattan, spending his teenage years in Queens.
[10] He is the author of SPS-1, SPS-2 IBM 1401 Symbolic Programming System, coauthor of 1401 Autocoder and participated in the 1401 Fortran II compiler project.
[citation needed] In 1968, Mokotoff left IBM to form his own software company with partner Stanley F. Smillie.
[citation needed] The Forward calls Mokotoff an "all-around makher (Yiddish for mover and shaker) in the Jewish genealogical world.
[16] Recognizing that there were many spelling variants of Eastern European Jewish surnames, even though they sounded similar, Mokotoff collaborated with Randy Daitch to create the Daitch–Mokotoff Soundex, system which provides a phonetic alternative to searching databases of names.
Originally published in 1991, with a revised edition in 2002, Judaica Librarianship calls Where Once We Walked, "the de facto print gazetteer of the shtetlekh of the Pale of Settlement.
[citation needed] In 1990, Mokotoff became a member of the board of directors of the Federation of Genealogical Societies (FGS).
[citation needed] In 2001, Mokotoff created the weekly e-zine of Jewish genealogy, called Nu?