There is much to be said about the Paladin class in Diablo 2. With all his auras and offensive skills, he is perhaps the most maligned class in the game due to overpowered he seems if given a good build. He can tank, but also do incredible damage. The auras make for some very interesting builds, as well as the very distinct offensive skills that are quite effective when used right. One of the weirder but really destructive ones is the Blessed Hammer.
When you look at the Blessed Hammer skill at first, you know right away that it is pretty weird. It is some sort of spiritual but corporeal hammer that slowly spirals away from the Paladin and hits whatever it comes in contact with. You can cast it multiple times and watch mobs around you disintegrate into piles of mush amid this tornado of hammers. It is quite a sight to behold, which is why the Hammerdin build is said to be the most played build in Diablo 2 as it can deliver up to 20,000 damage per hammer.
The basic Hammerdin build is all about maxing out 5 essential skills — Blessed Hammer (obviously), Vigor, Blessed Aim, Concentration, and Holy Shield. The 3 auras are chosen for their synergy with Blessed Hammer, while Holy Shield is for survivability. Meanwhile, you should allocate just enough Strength to use your gear, enough Dexterity to reach the maximum of 75% block, and put all other stat points on Vitality and none on Energy. Since you have Holy Shield, it should boost your 75% block to mitigate damage from enemies.
Another secret to the Hammerdin build is the Enigma Rune Word. By inserting the runes Jah, Ith, and Ber in that order, it not only gives a ton of bonuses, but also gives the Paladin +1 to Teleport (the actual skill). You can then teleport all over the place, as long as you have the mana for it. The Hammerdin can teleport next to a large group of enemies and launch Blessed Hammers to wipe them out. This made the Hammerdin a force to be reckoned with, so much that patch 1.13 sought to nerf Blessed Hammer by removing its ability to bypass Demon and Undead immunity.
But despite that nerf, all it really did was slow down the Hammerdin, especially when doing Baal runs. Undead enemies can still be damaged by Holy Bolt, even those that are immune to magic. That meant the boss pack of Achmel the Cursed, which was thought to be a problem for the Hammerdin at first when the patch first came about, turned out to be not that big of a problem at all.
There are plenty of variations to this build, both for vanilla Diablo 2 and for Lord of Destruction, mostly through the Diablo 2 items used with it. You can do a lot of things to maximize your damage or speed up your casting rate. There is plenty of information available online regarding the much-played Hammerdin, a build that is both interesting and powerful at the same time.