Donovan

Donovan is the Reilly's Rangers engineer first seen on the rooftop of the Statesman Hotel. If Donovan doesn't die during the Reilly's Rangers (quest) he will return to the Ranger Compound where he can repair your gear for less than the cost other merchants would charge.

Post-Quest random encounter
You can randomly encounter Donovan while traveling through the Capital Wasteland. Soon after he appears he should engage in a firefight against 3 Super Mutants (these can be Super Mutant Brutes or Super Mutant Masters at higher levels). When you talk to him, he will either thank you for your assistance (if you helped him kill the Super Mutants) or lightly chastize you for just watching the fight (if you don't assist him or talk to him before the Super Mutants appear). Regardless, he will give you a Mini Nuke and say that Reilly sent him.

After speaking with you, Donovan will make his way to Anacostia Crossing Station, and from there proceed back to Seward Square and the Ranger Compound. His exact route depends on where you encounter him, but he generally takes the long route all the way south to the Nuka-Cola Plant, then east past the Citadel, over the bridge, and through the southwest edge of the D.C. Ruins. It's not clear if he survives the journey if you don't escort him, since if you simply fast-travel to the Ranger Compound he's nowhere to be found (although he may simply take a very long time to walk there).

If the rangers are hostile to you, then Donovan will immediately begin shooting upon seeing you. If Donovan dies, he can be looted for a wrench simply called Donovan's Wrench worth 75 caps, however, the wrench is a quest item that fixes the Statesman Hotel elevator and cannot be dropped. He can also be looted for a unique Combat Helmet called the Ranger Battle Helmet that can be repaired with other Combat Helmets. The wrench does not weigh anything, so it adds no permanent weight.

Sometimes Donovan can be carrying very large numbers of Caps, as many as 3,000. This seems a fairly random happening, and is mainly when he's out alone in the Capital Wasteland. It may be that he is collecting the "float" from whoever is paying Reilly to map the Wasteland (the job you can pick up after the Reilly's Rangers Quest), or perhaps she likes to send her people out with the funds they need to survive? Nonetheless, you can loot these caps from Donovan with no loss of Karma if you track him at a distance, wait for him to run into some heavy opposition, take a few hits or die and then come to his aid (slightly too late, of course). If you are friendly with the rangers and loot Donovan when you encounter him in the wastes, expect the Rangers to be hostile on your next return to the compound.

Appearances
appears only in Fallout 3.

Related Quests

 * Reilly's Rangers (quest)

Bugs

 * (Xbox 360) Sometimes after the random encounter Donovan can be unresponsive, standing there doing nothing and not allowing to initiate dialogue with him. A possible fix is to wait for an hour in front of him, after that you should be able to talk to him. Make sure you initiate dialogue though, as sometimes he will run off without actually thanking you or giving you the Mini Nuke.
 * Donovan can actually be exploited for two Mini Nukes. First, talk to him before killing the Super Mutants and he will give you a Mini Nuke.  Then, kill the Super Mutants and talk to him again and he will give you another Mini Nuke