Linux is a free and open source (FOSS) monolithic kernel (which is evolving towards a modular kernel) originally developed by Linus Torvalds and released under the GNU Public License.
The Linux kernel was initially developed in 1991 on Linus Torvald's 80386 computer, and the initial versions were technically limited and only supported the i386 architecture. With contributions from dozens of other FOSS programmers, support for numerous features and architectures was added.
Linus originally started the project as an updated replacement for Minix, which was written by Andrew S. Tanenbaum to use as an example for an operating system design and implementation course. Many Linux distributions combine the kernel with many of the GNU utilities.