Simon Tatham (born 3 May 1977) is an English programmer known primarily for creating and maintaining PuTTY, a free software implementation of Telnet and SSH clients for Unix and Windows API platforms, along with an xterm terminal emulator. He is also well known as the original author of Netwide Assembler (NASM), and for his essay, "How to Report Bugs Effectively", which many software developers direct users to read before reporting bugs to them.
He also maintains a popular collection of small computer programs which implement one-player puzzle games. All of them run natively on Nintendo DS, Symbian S60, Unix (GTK+; Android, Mac OS X), and Windows.
He attended Cambridge University, and currently works at ARM Limited.