Erkenbrand was a warrior of Rohan during the War of the Ring as well as the lord of the Westfold. He can be recruited at a King's Camp and can lead one of various battalions into the field, making him extremely versatile. In addition he is trained at level 5. He is very similar to Elfhelm, Grimbold and the Rohan Captain. The battalion will not disband if the upgraded Marshal is killed, unlike the Thrall Master, but you will be unable to use the ability until they regenerate.
Erkenbrand can be given one of the following upgrades:
Soldiers of Meduseld - Call a battalion of Soldiers of Meduseld to serve as elite Swordsmen. Cost: 500
Wardens of Meduseld - Call a battalion of Wardens of Medused to serve as elite Pikemen. Cost: 600
Knights of Meduseld - Call a battalion of Knights of Meduseld to serve as elite Cavalry. Cost: 800
The strategy you use with him depends on the situation, what faction you are up against, etc. This is due to his special use of 3 different upgrades which give him 3 different kinds of elite units. The Knights could be used for spammy factions or factions with many archers, the Soldiers to counter enemy pikemen, or the Wardens for cavalry- based factions like Rohan. Also, once he dies and you revive him he is able to re-choose the battalion he will lead. He makes units fearless and can summon two battalions of the upgrade you chose, giving a chance to win the battle if the situation is dire.