The Other Reformation
On the other hand, on the Catholic side, the Church, at the time of Luther's exit, had already been undergoing a good 1500 years worth of fairly constant reform.
The first act of "reformation" seems to have been when St. Paul rebuked St. Peter over his change of habit to no longer break bread with Gentiles. Many other acts of "reformation" have taken place since. Some examples of individual reformers include St. Francis (13th century), who effected a reform by modelling Jesus's life in prioritizing the poor, the afflicted, the dispossessed and ignored. The very people the church structure was ignoring. St. Catherine of Sienna ended the Avignon papacy. It took some further bickering and the Ecumenical Council of Constance to resolve the issue once and for all. St. Charles Borromeo dealt with a rather scandalous church in Milan in the 1500s.
Corporate reform within the Church has also been an ongoing project through the means of the Ecumenical Councils. These councils have been responsible for clarifying (but never innovating) a number of Christian doctrines such as the Trinity, the nature of Christ and the like.
And reform continues, even up to the present day with Orthodox and Catholics working on ways to heal the East-West split; Catholics and Anglicans working towards reunification (very slowly!), from the Oxford Movement up to the establishment of the Ordinariate; the clerical sex abuse scandal and its sequellae; social reforms such as combating socialism, defending human life and even ways of battling climate change.
I think the take-away here is that, at least in the Catholic understanding, there is only one work of "reformation" and it is constant, be it on the individual level or on the broader level of matters of church governance and theological understanding. This is because the Church has always understood itself to be a divine organization with a bunch of fallible humans at the controls. Contrary to the idea of "proto-protestantism", Catholic reform is always done within the context of the apostolic faith and in the embrace of the Church founded by Jesus and not as a matter of irreconcilable revolt or dissent that leads to schism and separation and its sequellae, the ultimate devolution & abandonment of doctrine that follows. The precise opposite of what reformers are supposed to strive for!