Ryzen uses the "Zen" CPU microarchitecture, a complete original redesign by AMD that returned it to the high-end CPU market after a decade of near-total absence since 2006.

AMD's primary competitor Intel had largely dominated this market segment starting from the 2006 release of their Core microarchitecture and the Core 2 Duo. Similarly,

Intel had abandoned the Pentium 4, as its Netburst microarchitecture was uncompetitive with AMD's Athlon XP in terms of price and efficiency, and with Athlon 64 & 64 X2 they were outcompeted. Even an upgraded version of the prior Pentium 3 continues to underpin Intel's CPU designs to this very day.
Until Ryzen's initial launch in 2017, Intel's market dominance over would only continue to increase as simultaneously with the above top-to-bottom launch of the now famous "Intel Core" CPU lineup and branding,
the successful roll out of their well known "tick-tock" CPU release strategy. This brand new release strategy was most famous for alternating between a new CPU microarchitecture and a new fabrication node each and every year; with it becoming a release cadence Intel stuck to for almost an entire decade (specifically lasting from Intel Core's initial Q3 2006 launch with 65 nm Conroe, all the way until their 14 nm Broadwell desktop CPUs were delayed a year from a planned 2014 launch out to Q3 2015 instead.

This necessitated a refresh of their pre-existing 22 nm Haswell CPU lineup in the form of "Devil's Canyon", and thus officially ended "tick-tock" as a practice).

These events were incredibly important for AMD, as Intel's inability to further sustain "tick-tock" around 2014 would prove essential in providing both the initial and continually growing market openings for their Ryzen CPUs and the Zen CPU microarchitecture to succeed.