Someone who writes software or programs for computers is called a programmer. If you develop an application for mobile devices, you can also call yourself a programmer.
Programmers use a variety of computer languages to write the code (or instructions) that helps computers do the things their users want them to do. There are programmers who specialize in specific languages which are useful in various industries — some are used by financial institutions and others by scientists, for example. Evidence of the dramatic way things change over time is clear from the shift in this word's meaning: in 1890, a programmer was an "event planner."