While Breaking Bad may be remembered primarily for portraying Walter White's descent into his Heisenberg persona, the flawless execution of Better Call Saul proved that the original show's quality wasn't all because of its main antihero protagonist. Since Better Call Saul was a prequel to Breaking Bad, it revolved around side characters featured in Breaking Bad, including Jimmy McGill, aka "Saul Goodman," Mike Ehrmantraut, and Gustavo "Gus" Fring. While those three resonated with fans, there was no guarantee that elevating them to main characters would be a good decision.

https://screenrant.com/better-call-saul-returning-breaking-bad-characters-good/