Many Japanese find this phrase very exhilarating. It is a metaphor for a hero/heroine/mighty warrior who vanquished many opponents alone.
一(ichi)=one or single
騎(ki)= cavalryman/trooper/horseman
一騎(ik-ki) = It literally means single cavalryman/trooper/horseman.
On the other hand,
当(tou)= This Kanji has a lot of definitions when used alone. It has two main definitions. First, it means “to hit” and second is “equal”. The latter is the most appropriate for this context.
千(sen)= It literally means “1000”. However, it is not only limited to 1000 but it may also mean ‘many’.
As a result,
一騎当千= It’s a hyperbole which demonstrates someone whose power or strength is equal to 1,000 opponents. In other words, having unbelievable and unthinkable power.
We may not defeat opponents like warriors or soldiers in the movies but I believe, we are all heroes in our own ways. We survived insurmountable adversity in life brought by Covid-19 pandemic.
If you are interested in these Kanji, you may simply copy them from this website and use them as you please. Make them yours!