  Recent years witnessed rapid progress of chip-scale integrated optical
frequency comb sources. Among them, two classes are particularly significant --
semiconductor Fabry-Per\'{o}t lasers and passive ring Kerr microresonators.
Here, we merge the two technologies in a ring semiconductor laser and
demonstrate a new paradigm for free-running soliton formation, called
Nozaki-Bekki soliton. These dissipative waveforms emerge in a family of
traveling localized dark pulses, known within the famed complex Ginzburg-Landau
equation. We show that Nozaki-Bekki solitons are structurally-stable in a ring
laser and form spontaneously with tuning of the laser bias -- eliminating the
need for an external optical pump. By combining conclusive experimental
findings and a complementary elaborate theoretical model, we reveal the salient
characteristics of these solitons and provide a guideline for their generation.
Beyond the fundamental soliton circulating inside the ring laser, we
demonstrate multisoliton states as well, verifying their localized nature and
offering an insight into formation of soliton crystals. Our results consolidate
a monolithic electrically-driven platform for direct soliton generation and
open a door for a new research field at the junction of laser multimode
dynamics and Kerr parametric processes.
