Leadhead Splicer

A real pain in the backside at just about any point throughout the game, especially at harder levels, the first Leadhead Splicers you'll encounter in BioShock are just packing pistols, but upgrade to machine guns at around the halfway point, making them a whole lot more deadly. Worse still, they boast a ridiculously high tolerance to lead, so plasmids and other inventive means of killing are almost required, and highly recommended. For example: Grab his mask using Telekinesis and punt it back at him for an instant kill on the easier difficulties. This isn't very easy, though.

Strategy
Cannon Fodder? - Hardly, these scumbags are tougher than a tramp's skid mark later in the game (especially on Hard), sucking up dozens of bullets at a time. Couple this with a very agile attack pattern, ducking and weaving like crazy, getting into cover to reload, running to Health Stations and their tendency to attack alongside Thuggish Splicers makes them a force to be reckoned with.

Weapon of Choice - Telekinesis plasmid is perfect for the job here, as for all their tolerance to bullets, smacking 'em in the face with a ballistic wheelchair drops them like a sack of potatoes. Failing that, incapacitating them with ice or lightning, then following up with a powerful wrench attack is just as good, but loses you those precious, precious bullets, as Leadheads tend to be good for finding rare ammo types.

It is not clear what these splicers are exactly spliced up with, as no gene tonic or plasmid that Jack can obtain affects his prowess with firearms. However, the splicing might explain their tolerance to bullets.

Notable Leadhead Splicers
Only one Leadhead Splicer plays a significant role in the story: Dr. J.S. Steinman, the mad king of the Medical Pavilion. Dr. Steinman is notably also the first Leadhead to use a machine gun rather than a pistol, as the normal Leadhead Splicers don't start picking up machine guns until roughly around Hephaestus.