Solar Paladin

The Solar Paladin is the first boss unlocked through rankup, and is unlocked upon reaching the Elder rank. This is one of the easiest bosses to defeat, and can be completed easily with T1 gear and some food.

Unlocking
Once you unlock the Elder rank, in order to be able to fight the Solar Paladin you must talk to the NPC Gerald, located in the rankup area of the spawn. Upon talking to Gerald he will give you the quest "Elder Rank Up". This quest requires you to read through some dialogue, and pay him 5000$, a feat which is easy even for beginners. Once you complete this quest, you gain access to the command "/warp eldermission" which teleports you to the arena where you can fight the solar paladin.

Rewards
Upon defeating the Solar Paladin for the first time you will be rewarded with a Solar Core which can be traded at the Mesa Landmark for your pick between a Solar Molar, Hermes Boots, and a Righteous Barrage. You only ever get one Solar Core so you have to choose wisely. The secondary reward to defeating the Solar Paladin for the first time is that you complete the quest "Special Mission: Elder Rank"