Hennadii Stepanov has been contributing code and review to Bitcoin Core since 2018, and Brink describes him as one of the most prolific contributors to the project in that time. His grant funds full-time work on development and review.
He maintains the Bitcoin Core graphical interface and the translations. Both sit at the edge of the project where most users actually meet it, and both are maintenance rather than invention: the GUI lives in a separate repository whose master branch is kept identical to the main tree, and translations have to keep pace with every release across the languages the project ships.
Bitcoin Core's own description of the maintainer role is narrow by design. Maintainers hold commit access and merge patches the contributors agree should be merged, acting as a final check that a change is safe and in line with project goals, and the role exists by agreement of project contributors rather than by appointment.