Phoenician mem — "water", through Greek mu.
M
mem was a wave. The shape of M is that same outline of water, frozen three thousand years ago. Greek called it mu and gave it the numeric value 40; the Cyrillic М kept both the shape and that number.
Adams · Armstrong · Cameron · Campbell · Chambers · Chapman · Coleman · Colombo · Cunningham · Freeman · Gomez · Graham · Guzman · Hamilton
In the modern alphabet this letter is number 13 of 26. Before it comes L, after it N. 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 29 and closes 2. Among the 96 given names in the base it appears in 21. The surname carrying the most of it is Zimmermann, with 3.
James · Michael · William · Thomas · Matthew · Mark · Timothy · Benjamin · Samuel · Adam · Liam · Mary
These letters came from the Greek alphabet.