Greek delta, before that Phoenician daleth — "door".
D
the river delta is named after the shape of this letter, not the other way round: Herodotus saw the Nile's mouth and said it looked like a Δ.
Adams · Anderson · Andrews · Arnold · Boyd · Bradley · Chandler · Crawford · Daniels · Davies · Davis · Delaney · Delgado · Diaz
In the modern alphabet this letter is number 4 of 26. Before it comes C, after it E. The order itself is inherited: Latin took it from Greek, Greek from Phoenician, and the sequence has survived largely unchanged for about three thousand years. Every rearrangement since has been an insertion, not a reshuffle.
This is a consonant: it sets the hardness of a name and how it meets the next word. In a corpus of 315 surnames this letter opens 14 and closes 15. Among the 96 given names in the base it appears in 14. The surname carrying the most of it is Delgado, with 2.
David · Richard · Daniel · Andrew · Edward · Alexander · Adam · Amanda · Diana · Douglas · Raymond · Linda
These letters came from the Greek alphabet.