A man from an ancient and fallen empire who is cursed with undeath, and forced to permanently wander in search of a way to undo his curse, but tragically losing his memory and sanity with each encroaching death. He is basically clinging onto hope by searching for those who still have their mind intact.
Basic concept: A lot of random abilities and can come back to life, but loses an ability with each death.
First level you roll roll 1d100 three times. First one from this table, second one from here, and this is the third one. Exact details to be determined by DM to adjust from original source to better fit the Ruin Knight. Make sure to write down which abilities get rolled, even if it's just a bonus added somewhere else on the character sheet. At each level after 1st roll 1d100 on one of the tables.
Whenever the Ruin Knight reaches 0 HP they die. After 1d6 rounds the knight comes back to 'life' with one less ability. The ability that gets lost is rolled randomly. If the knight dies with no abilities, the character is lost. The knight will rise again somewhere sometime in the future, but for now the player must roll up a new character.
All equipment that a Ruin Knight carries around is affected by the curse that traps them in undeath. Metal rusts, leather rots, etc. Nothing every completely breaks but anything the knight carries for longer than a few hours shows obvious signs of damage and anything carried for a few days looks like it's about to break. All armor, even crappy armor, is treated as average for purposes of breaking on a critical hit. All armor becomes crappy after being worn for a few days. Any hit that would break a piece of armor completely can be instead put on another piece of armor the knight is wearing.
Ruin knights don't need to drink, but do need to eat meat semi-regularly to keep themselves from becoming mindless undead.