He saved many NCR troopers during the Battle of Nelson. An uncompromising individual, he is not pleased by the Legion's use of NCR hostages to discourage attacks, and believes that killing them is the only way to get his troops to retaliate.
He will warn the Courier of the danger up ahead, as Caesar's Legion has captured the nearby Camp Nelson (if they have a high reputation with the NCR he will let them through).
Milo will joke about a "few dozen" doses of Psycho (24), claiming it would get the weepy soldiers moving down the hill to attack, but if the Courier actually has the Psycho, he will say he is impressed but was only joking.
He will also remark upon the reputation the Courier currently has with the NCR when they introduce themself. He seems to look down on the NCR troopers, considering them inferior.
He has named his cowboy repeater "Carmine," but it is just a standard repeater.
In dialogue with him, one can choose to identify the Courier by name, one of the rare cases in the game where the Courier's name is used.
If the Courier's Intelligence is lower than 4 when first meeting Ranger Milo, he will inform them that some "Legion snakes" are held up in Nelson to which the Courier can respond 'Snakes are small. Why don't you just use a gun or whatever to shoot them." He will then call you a "special folk" and explain that they are not really snakes but "like snakes."