Carl Hialmar Rendahl (born Jönköping 26 December 1891; died Stockholm 2 May 1969) was a Swedish zoologist, cartoonist and painter.
He is most famous in Sweden for his authorship of Fågelboken, the "bird book" which sold 60,000 copies.
As a student, he worked as a freelance journalist, mainly writing popular science articles, and he also translated books into the Nordic languages as well as publishing drawings.
He was the editor for the series of 12 books called Vi och vår värld ("Us and our World"), two of which he wrote.
He also studied the fish collected in Australia by the Swedish expedition led by Eric Mjöberg and by the Norwegian Knut Dahl, describing several new species from each.