Akira from Devilman, Kouji from Mazinger Z, Hiroshi from Koutetsu Jeeg, Ryoma from Getter Robo all unsurprisingly look similar.

Akira, Kouji, and Hiroshi were characters created by Go Nagai and Ryoma was created by Ken Ishikawa, a close friend of Go Nagai. All four series were animated by Toei.

But we can go further.

Hyouma from Chou Denji Robo Com Battler V, Kenichi from Chou Denji Machine Voltes V and Kento from Mirai Robo Daltanias all look alike. Neither of these three are Go Nagai however they are all Toei.

If you see the pattern, Go Nagai Sideburns with shaggy dark hair was the thing for super robot anime protagonists. Takeru from Magnerobo Ga-Keen, Takeshi from UFO Senshi Dai Apolon, Tetsuya from Great Mazinger, Sanshirou from Daikuu Maryuu Gaiking, Keats from Kikou Kantai Dairugger XV, Takashi from Video Senshi Lezarion, Akira from Hyakujuu-Ou GoLion, Akira from Yuusha Raideen, Ryger from Uchuu Majin Daikengou... I could go on.

There's a few exceptions that I can think of off the top of my head. Kappei from Muteki Choujin Zanbot 3 who had the start of sideburns but close cut hair, Goro from Chogattai Majutsu Robot Ginguiser who had sideburns but close cut hair, Banjou from Muteki Koujin Daitarn 3 had sideburns and shaggy hair but it was blue