Augustin-Louis Cauchy (1789-1857) presents the Cauchy integral theorem for general integration paths - he assumes the function being integrated has a continuous derivative.
Citation:
Editors. "Cauchy integral theorem postulated".
The Literary Encyclopedia. First published 01 May 2009
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6258, accessed 23 May 2013.]