Gustaf Johan Billberg (14 June 1772, Karlskrona – 26 November 1844, ) was a Swedish botanist, zoologist and anatomist, although professionally and by training he was a lawyer and used science and biology as a hobby.
In 1790 he earned his legal degree in Lund, later working as an auditor at the audit chamber in Stockholm (from 1793). In 1798 he became an "landskamrerare" (member of the county administrative board) in Visby. In 1808 he returned to Stockholm, where from 1812 to 1837, he served as "kammarrättsråd" (member of the administrative court).
He was elected member of the Royal Swedish Academy of Sciences in 1817.
Billberg was the author of the following works:
The plant genus Billbergia was named for him by Carl Peter Thunberg.