"L" is lich. At level 34, you will be able to turn into a "Lich". I assume you are a Death Disciple right now... Here's the list of "Lich" monsters you will be able to get, and at which level:
37: Crypt Thing
39: Monastic Lich
41: Master Lich (with undead summoning ability, hope you have some Leadership skill!)
42: Iron Lich at 42(elemental melee damages, also undead summoner, BREATH ATTACK!!!)
45: Lesser Black Reaver(strong, but no summons.)
54: Demilich(strong, ability to summon masses of strong undeads!)
64: ArchLich(stronger, lots of spells, even more summoning powers!)
71: Black Reaver(stronger in melee, but not as good at summoning, more limited magic abilities. Still strong though...)
It is important to know, when playing as a monster, that just because you can "evolve" into another creature doesn't mean the "evolved" creature will be better. For the Liches, here's the ones I think you should consider, depending on your character's build:
Iron Lich: 3 elemental melee attacks at 5d6 is nice, it has summoning powers, ball spells for Fire, Cold, Electricity and Water, Cause Critical Wounds and a FIRE BREATH ATTACK(at 28d100 hp), making the Iron Lich the best magic attacker amongst the Liches. You can also get this one at level 42, which is pretty early compared to the other good liches.
PROS: Elemental melee attacks(Fire, Cold and Electricity), fire breath attack, undead summoning, other ball spells, 28d100 hp is pretty good for that level.
CONS: No blinking/teleport abilities like other liches, must rely on summons to beat magic immune enemies, in the long run 5d6 for melee damages might be a bit low.
ArchLich: Summon masses of high undeads, can summon kin, demons and weaker undeads if needed. Add a nether ball, cause critical wounds, teleporting and healing powers, two strong damaging melee attacks at 13d12 and 50d100 hp, and you have quite a solid and versatile monster here. If you like summoning powers, then definitly pick the ArchLich, it's the best at that!
PROS: Best summoner amongst the liches, good hp, lots of nice spells.
CONS: No breath magic attacks, only two damaging melee attacks.
Black Reaver: Four melee attacks(two at 12d8 and two at 8d6), 75d100 hp, mana and nether ball spells and minor undead summoning abilities. Highest hp amongst the Liches, 4 good melee attacks, and nice magical abilities to complement that. While not as good as the ArchLich at summoning, and lacking some of the ArchLich's good spells, such as teleport and healing, it is probably a better choice if you didn't raise Leadership skill(or don't plan to), and if you go melee.
PROS: Strongest melee attacker in Liches, highest hp, mana balls and minor summoning spells, which can still be useful.
CONS: Lacks the ArchLich's large array of spells, no teleporting, level 71 is pretty late in the game.
Now, which one to choose? If you want to focus on magic attacks, the Iron Lich is the way to go. If you want a large array of spells and like summoning all kind of creatures, then pick the ArchLich(and make sure you have some Leadership skill!). Finally, if you want to go melee, then pick the Black Reaver. Of course, this is only my opinion. Iron Lich and Black Reaver still have some summoning powers, and feel free to choose them for summoning. ArchLich has two melee attacks at 13d12, that IS strong, so it can go melee as well.
Anyway, that's it. Pick your Lich wisely, and have fun!