What operating system did Linus Torvalds use while developing Linux?

Development was done on MINIX using the GNU C compiler

MINIX seems to be the OS used by the Intel Management Engine that’s embedded inside all modern Intel CPU’s and is basically its own system that “oversees” all activity on the PC.

Source: Paul Serdiuk’s answer to What operating system did Linus Torvalds use while developing Linux? – Quora