Caspar Wessel was a Norwegian surveyor whose mathematical fame rests on a single paper, published in 1799, which gave the first geometrical interpretation of complex numbers. His priority in this discovery, however, went unrecognized for many years. Thus what should really be called a Wessel diagram is known instead as an Argand diagram after the man whose work on the same subject, published in 1806, first came to the attention of the mathematical world. Wessel's paper, by contrast, wasn't noticed by the mathematical community until 1895 when the Danish mathematician Sophus Juel drew attention to it and, in the same year, Sophus Lie republished Wessel's paper. Astonishingly, Wessel's remarkable work was not translated into English until 1999 – its bicentenary!