Protector Casdin

Protector Henry Casdin is the leader of the Brotherhood of Steel Outcasts in the Capital Wasteland. According to Elder Owyn Lyons, he was one of the best fighters in the Capital Wasteland Brotherhood of Steel before he took other Brotherhood members and formed the Outcasts in order to continue the original mission. He trades the Lone Wanderer for technology that is acquired across the Wasteland and in return gives out useful supplies that the Outcasts' possess in abundance (see Technology scavenging below).

If you bring him any Outcast Power Armor or Outcast Power Helmets, he will take them from you without giving anything in exchange. However, he won't take away Linden's Outcast Power Armor if you have it with you when you talk to him.
 * Exception: If you have an NPC companion who can carry gear for you, and you give them the Outcast armor, Casdin will not take it from them.

Protector Casdin can be found standing at the entrance to Fort Independence, the Brotherhood Outcasts headquarters. He holds the key to Fort Independence. The player can unlock the side quest of scavenging for technology by first speaking with Defender Morgan.

Once a sufficiently large amount of technology has been traded the Lone Wanderer is told that they are considered friendly by the Outcasts. This allows for infiltration of Fort Independence without encountering the hositility of the residents.
 * Just to be clear, you still have to pick the lock to get in, and will loose Karma in the process, but once in, the Outcasts will not attack you.

Technology scavenging
You can trade some pieces of power armor (normal Power Armor and Helmets, Tesla Power Armor, and Enclave Power Armor and Helmet, but not Tesla Helmets, the T-51b Power Armor and helmet, the Prototype Medic Power Armor, Brotherhood Power Armor and helmets, Lyons' Pride Power Armor, and Outcast Power Armor and helmets), any type of energy weapon (including the Alien Blaster, but not other unique weapons or the Gatling Lasers), sensor modules, and scrap metal. In return he'll give you either of these, in accordance with the perceived value of the item:
 * 5.56mm ammunition
 * Frag grenades
 * Rad Away
 * Stimpaks

Technology Scavenging Value Table
† Scrap Metal must be traded in groups of two; Alien Power Cells must be traded in groups of twelve.

Trivia

 * Should the player give Casdin a Enclave Advanced Power Armor Mk II, Enclave Advanced Power Helmet Mk II, or Tesla Power Armor, Casdin will wear them. He would wear the Tesla Power Armor more than the Enclave Power Armor and he would wear the Enclave Power Armor and Helmet more than his own Outcast Power Armor. This can be rectified by using console commands to have him equip his Outcast Armor back.

Bugs

 * There is no option to give him a Tesla Power Helmet
 * You also can't give him a Gatling Laser, though this may be due to its classification as a big gun
 * If you give him the Alien Blaster, kill him, and take it off his corpse, its condition will be restored to 100.