Demoman
Mr High Explosive.
Advantages
Can deal out incredible amounts of damage rapidly.
Disadvantages
Lack of armour, slow reloads.
Health
90
Armour
120 (spawns with 50)
Typical role
Defence or offensive support.
Notable Weapons
Grenade Launcher
Delivers lots of damage to short ranges very rapidly. The grenades bounce around corners, allowing the demoman to engage targets without making himself visible. Also works well underwater, unlike thrown grenades.
Pipebomb launcher
The addition of a controlled detonation makes this very effective in skilled hands. A grenade that would otherwise be an ineffectual miss can be detonated as it passes the target. These can also be used to lay minefields in strategic bottlenecks, which can then be detonated when an enemy attempts to pass.
MIRV Grenade
One of the deadliest weapons in the game. The initial explosion is comparable to a regular grenade, and scatters the four submunitions. These, in turn, each explode with somewhat more force than a regular grenade. A single MIRV will kill a level 3 sentry gun outright from 3 or 4 yards away. Most classes will meet a similar fate at ranges of 5-6 yards. Most experienced players will simply run for cover when one of these comes into view, which makes this an excellent area denial weapon.
Offensive capacity
Lots. In skilled hands, the grenade and pipebomb launchers are deadly short-range weapons. The demoman also spawns with a full stock of grenades, including the deadly MIRVs, which means he can cause incredible havoc within an enemy base. Not for nothing is this class also known as the "demospam". Caution should be applied, though - in unskilled hands, the demoman can be a nuisance to his own team, too; his grenades are much less discriminating than most other weapons, due to their tendency to bounce around. The Demoman's team-mates will not be amused if they are constantly having their armour stripped off by indiscriminate grenade barrages. The Detpack is also an essential tool on maps such as The Well and The Rock. The demoman's load of high explosives makes him good at removing enemy sentry guns - the MIRV, in particular, is very effective.
Defensive capacity
Again, considerable. A well-set pipebomb trap can turn a bottleneck into a deathtrap. A good trick is to try to scatter the bombs around a bit - this means you can hit a much larger area when you detonate them. Which, in turn, makes it much harder for fast classes (such as scouts) to get past.
How to fight them
Stay at long range - the pipebomb/grenade launcher only has a range of about 20 yards, and is only really effective for half of that (unless they're VERY good). Alternatively, close to point-blank range - a demoman may be reluctant to use the grenade launcher at at close range for fear of the blast damage, and the pipebomb launcher has a minimum range of several yards, due to the arming time of the pipebombs. The Demoman's heavy load of high explosives makes them particularly vulnerable to EMP grenades.