By whom? The code doesn't magically merge itself. Which individuals are responsible for the merging?
Wladimir, Pieter Wuille, Marco Falke, Jonas Schnelli all have commit access. The may be more. I'm fairly certain they all got their merge access before Wladimir was maintainer.
Originally Satoshi Nakamoto was the only one with merge access. When he left, he gave that access to Gavin Andresen. Gavin maintained sole merge access until he left when he gave that access to Wladimir. That was the last I heard. I'm not doubting that Wladimir gave that access to additional individuals, I'm just curious to know when, why, and to whom. It seems like important information to know if we're going to put our faith in a codebase.
The may be more. I'm fairly certain
I'm looking for actual knowledge, not guesses based on what you thought you might have heard at sometime in the past from some unknown source.