Katherine is one of the oldest, most diverse, and all-around best names: it's powerful, feminine, royal, saintly, classic, popular, and adaptable. Long one of the top girls' names starting with K, Katherine has now been unseated on the popularity list by upstarts Kennedy and Kinsley, but a dip in popularity only adds to its charm.

Callahan, the simpler spelling of Callaghan, is a rhythmic jig of a name whose history harks back to the ancient King of Munster. In the Dirty Harry movies, the Clint Eastwood character is Harry Callahan.

Typically used as a short form in Sweden and as a given name in Finland, Estonia, and Denmark, Kalle is a variation on Karl, in turn, making it to Charlie from Charles. Pronounced KAL-leh in Swedish and as KAHL-leh in Finnish and Estonian, notable bearers include racing driver Kalle Rovanperä, content creator Kalle Flodin, and film maker and activist, Kalle Lasn.