It was probably Bishop Ulfilas who created the Gothic letters in order to produce a translation of the Bible into the Gothic language. As in the case of the runes, there have been scholars who claim that Ulfilas' letters have been developed from a single source. Kirchhoff (1854) claimed that the origins of all Gothic letters are Greek, and Zacher (1855) maintained that Ulfilas created all the letters with Latin counterparts in mind (Braune 15-16). Later on, scholars tended to agree that the letters are mainly of Greek origin, with the exception of some letters that must be of runic and Latin origin (ibid.). However, there are still scholars like Ebbinghaus (Braune 16) who maintain that the origins of the alphabet are to be viewed as monogenetically Greek. Wimmer (1887), Gutenbrunner (1950), Mossé (1950) however all agree that the Gothic alphabet must be viewed as a synthesis of two traditions, namely the "latino-graeca" and the "runo-graeca" (ibid.) Most letters are seen as Greek by the majority of scholars, but the origin of some letters, e.g. the symbols for /f/, /j/ and /u/, is controversial (Braune 16).
Actually, the Greek alphabet had no letter for /j/ and there was no /j/ in the Greek of that time, and the Latin letter I stood for /i/ as well as /j/. So the Runic /j/-letter was an obvious choice. The Latin V was ambiguous, unlike the runic /u/-grapheme.
Both the letter forms and phonetic facts can be used as evidence against monogenetic theories. There are many other alphabets derived mainly from Greek that also have a few letters of different origins, e.g. Coptic (DB 287), Armenian (DB 366) and Glagolitic (DB 347), the script from which the Cyrillic was derived.
Braune, Wilhelm. 1981. Gotische Grammatik. Mit Lesestücken und Wörterverzeichnis. 19. Aufl., neu bearbeitet von Ernst A. Ebbinghaus. Tübingen: Max Niemeyer Vlg.
Daniels, Peter T. and William Bright. 1996. The world's writing systems. NY and Oxford: OUP 1996. (=DB)
Important note about the alphabet table below: The Unicode encodings for Gothic script were not a part of the official Unicode standard at the time of this writing. They may need to be revised once Gothic script is standardized.
See also Gothic language