The 1890 "Russian Flu" pandemic is now believed to have been caused by one of the common cold Coronaviruses, HCoV-OC43. At the time of historical pandemics, there was no way to identify the infectious agent, though. So connecting the pandemic to the virus is based on descriptions of symptoms, and patterns of which demographic groups were most affected; as well as genetic analysis to estimate when the virus jumped from animals to humans.
Accounting for expected mutation rates and working backwards, they calculated that the jump into humans occurred around 1890.
That date isn't the only thing linking OC43 with Russian flu. Many patients of that pandemic had pronounced symptoms affecting their central nervous system. Today, although mostly associated with mild colds, OC43 is also known to infect nervous tissue.
It's likely that all of the common cold Coronaviruses caused pandemics when they first started infecting humans. For the others, that happened much longer ago than OC43, so the historical record is less detailed, and there is more uncertainty in the genetic analysis.
In fact, it's possible that many or even all of the viruses that currently circulate among humans without problems were much less benign when they first emerged.
Another example is the outbreak of severe symptoms from Zika infections in the Americas when the virus arrived there, after circulating in humans for (at least) decades in Africa with only mild symptoms:
In the outbreaks reported up to 2013, most of the infected patients were asymptomatic and only 20% of them had mild symptoms such as fever, arthralgia, maculopapular rash, and conjunctivitis.
So it's suspected that many "harmless" viruses were worse when they first emerged into humans, but with the tools that are currently available, there is no way to establish definitively whether any particular virus caused major pathogenic outbreaks in the past.