Plenty of people are excellent individually and leave everyone around them exactly as they found them. A much smaller number consistently make the people they work with sharper, more confident, and better at their jobs, often without a formal role that requires it. That second group is who people mean when they call someone a real leader, title or not.
This doesn't require teaching classes or running a mentorship program. It usually shows up in small, repeatable moments: taking the extra ninety seconds to explain the reasoning behind a decision instead of just the decision itself, so the person you're talking to learns something transferable. Asking a question instead of handing over the answer, so someone builds the muscle of figuring it out rather than just executing your instructions. Noticing a specific strength in someone before they've noticed it themselves, and naming it plainly enough that they start to believe it too.
A colleague asks you to just fix a formatting issue in their document. Instead of quietly fixing it and moving on: "Fixed it, the trick is the table's inheriting styles from the section above, so anytime that happens you'll want to check the parent block first. Worth remembering for next time." Ten extra seconds, and the next time it happens, they don't need you.
Making other people better also means being willing to give feedback that's genuinely useful, even when it's easier to stay quiet. Most people default to withholding a hard truth because it feels kinder in the moment, but withholding it usually isn't kindness, it's avoidance, and it deprives someone of information they needed to actually improve. The people who consistently make others better are often the ones willing to say the slightly uncomfortable thing, delivered with enough care that it's clearly meant to help, not to criticize.
There's a selfish reason to build this habit too, beyond it simply being the right way to treat people: a team, or a network of colleagues, that's genuinely gotten better because of working near you becomes a durable source of trust and opportunity that follows you for years, people remember who helped them get sharper, and that memory tends to outlast almost anything else about a working relationship.
None of this requires being the most senior person in the room. It requires noticing, in the moment, whether your interaction with someone is going to leave them exactly where they started or slightly more capable than they were five minutes ago, and choosing, consistently, the second option.