Already the all-time leader in strikeouts, Nolan Ryan became the first pitcher to ever record 5,000 strikeouts when he fanned future Hall of Famer Rickey Henderson on August 22, 1989.
Now 25 years later, that looks like a mark that will never be reached again, and it's not the only milestone that may never be touched.
For the sake of argument, we'll consider the modern era to be everything that happened after the 1919 season.
It was 1920 when Babe Ruth officially put the dead-ball era in the rearview mirror, launching an unheard-of 54 home runs, nearly doubling his previous record of 29 from the year before.
So here is a look at seven modern-day MLB milestones, including the 5,000 strikeouts Ryan piled up, that will never be reached again.
These seven represent a good mix of single-season and career marks, and cover both the pitching and hitting side of things. A case can certainly be made for a number of others to be included, but these were the most statistically significant in my opinion.