Solo Class

Games in which An Adventurer Is You usually design (or aim to, at any rate) their Class and Level System so that each class only excels in one particular niche and and the whole of a party is always greater than the sum of its parts.

Some designers realize, however, that there are gamers who play alone for various reasons and tailor certain classes to this preference. These are classes that enable an average player to one-man encounters that others usually cooperate to overcome, but they usually do so less efficiently than a party of specialists. New players will often be encouraged to start with this type of character so that they can find their favorite activities and style of play without having to fish around in the community for teammates. In an offline or single player context, this type of class can familiarize a newbie with the game's mechanics before introducing synergies and group coordination.

Solo classes often fall into two broad categories:

Type I: Classes specializing in solo play:

The Jack of All Stats, with limited versions or equivalents of enough specialists' abilities that they can keep themselves alive and barely defeat stronger or more numerous enemies without help. Besides striking out on their own, they can be less capable replacements for multiple types of specialists—e.g. becoming a secondary healer or an off-tank.
The Minion Master, The Turret Master and any class that can almost create their own party out of thin air to back them up.
The Shapeshifter who can assume the optimal specialist role for any situation.
Hunters and hunter-like classes, whose Real Life counterparts are typically portrayed as being masters of the wilderness. With powerful ranged attacks, debilitating traps, abilities that facilitate escaping from tight spots and a strong animal companion, the hunter class are usually a game's designated loners.

Type II: Party-centric specialists whose niches enable solo play: Note: The following list contains just a few of the possible examples as solo ability depends on how a specialist's niche is defined in a given game.

Meat Shields with relatively decent attack power may be able to withstand Mook assaults and whittle down bosses without their usual backup but take an age to complete the encounter.
Healers with access to instant self healing and token offensive spells may be able to grind down armies or bosses on their own while topping up their health but lack of offensive ability causes the encounter to drag on.
Nukers with sufficient spell power and space to distance themselves from their target(s) may be able to kite enemies to death before their meager defenses give out. They may also have the option of casting multiple layers of temporary magical defense on themselves and 'bursting' down enemies while protected.
Gradual Grinders can pop a bunch of Standard Status Effects on a boss or group of enemies and run around until they drop if the game mechanics allow it... usually not for long.

A solo class that doesn't need a party in any situation may be a Game Breaker. Balanced ones may be resented by Scrubs who feel that they encourage 'Noob-ish' play and are hard to integrate into a team strategy. Classes that can fly solo to any extent in team or open PVP are often Base Breakers. The Solo Character Run is usually not done using one of these as it would be less of a challenge.

Note that all classes in most games can be played solo with sufficient skill, enough Level Grinding or Good Bad Bugs so this trope only refers to classes that are easier to play solo than others (e.g. a new player can solo to level Cap without ever joining a party on these classes but not others) or that the developers intended for that purpose.

Examples of Solo Class include:

Dragon Age: Origins lets you do this several ways. First is the Arcane Warrior, a heavily armored mage who gets abilities that allow them to seriously reduce or totally nullify all damage and they also have access to heals and powerful offensive spells. Then there's the rogue. Properly built, a rogue can become essentially immune to melee damage, and resist all but the most powerful spells.
Adventure Quest Worlds has the rogue and the pirate, whose Footwork skill allows them to dodge enemy attacks (and every attack you dodge gets you a little bit of health back), and whose DPS abilities can even allow them to take out bosses solo, especially when Concealed Blade kicks in. The Healer can also solo, but it takes a while and it's limited to how much mana you have and can get back from Energy Flow.
- Many Rank 10 faction classes, such as the Necromancer, the Undead Slayer, the Troll Spellsmith, the Skyguard Grenadier and others are quite capable of soloing bosses. There's also the Paladin, which combines good combat ability with good healing ability.
In City of Heroes, the Scrapper is the local soloist-class—striking a good balance between absorbing damage and dishing it out, a well-built Scrapper can solo anything short of a full-on Arch-Villain. (And sometimes even that—depending on the version. Early versions had a few exploits that certain builds of scrappers could use to become virtually immortal at higher levels.)
In City of Villains, the Brute can play pretty much the same role, but the real solo-master there is the pet-centric Mastermind-class, who basically get to bring their own army with them wherever they go. At higher levels, you'll have anywhere from 6 to 8 pets following you around (depending on exact powersets), making it quite possible to handle most bosses on your own—without even getting your hands dirty.
In Team Fortress 2 some of the classes can do their job on their own (for example an Engineer can set up a sentry nest and a Sniper can find a good vantage point, while a spy can infiltrate on their own). Of course the game is deliberatly designed so that having a team mate back them up always helps (e.g. a pyro to guard an engineer or sniper from a spy, or a group of offensive classes to rush the enemy when the spy begins sapping their sentries).
Many classes in Flyff can solo due to Good Bad Bugs or a Gamebreaker. However, the Billposter is usually considered the purpose built solo class due to high damage output combined with decent endurance and the ability to self heal (as an offshoot of the basic healing class). The Battle Priest (A Priest built for fighting instead of healing and using Billposter equipment) is another 'proper' solo class.
Maple Story infamously has the Clerics and their Prestige Classes being the best solo classes after a certain level as their heals damage undead enemies while affecting themselves as well. Their final job gains the ability to nuke several entire platforms at once, which still puts them ahead of other fourth jobs even after a damage Nerf.

HP priests (priests gearing for HP, which increases durability without sacrificing too much damage) especially could shrug off most enemy hits and heal wounds well enough to keep going. With MP Restore before the Big Bang patch it was possible to wait about a second or so and restore roughly 50 mp during a battle, never using pots or Magic Guard. The patch removed this feature, though (which also had the side effect of making chairs completely ineffective for mage classes).

Several WoW classes have gained and lost this designation due to Blizzard's constant rebalancing, though Hunters, Paladins and Death Knights have been especially persistent examples in players' eyes. The discovery that any class can solo group content at its original recommended level is usually followed by calls for a Nerf.
Hunters can solo very efficiently in Eden Eternal due to having most of their DPS come from a powerful tiger companion that can be healed (they are sub-par against bosses that quickly kill or dispel their tiger). The class is exceptionally popular with botters for this reason.
A Cleric in Neverwinter Nights 2 can handle just about anything the game can throw at it by level 7, or Level 5 with the proper Domains. Once he learns the Divine Power buff, a Cleric can fight better than a Fighter or Barbarian, with as-good-or-better armor, more hit points, efficient healing, and a bevy of available buffs, albeit with a slightly worse weapon selection (which can be remedied by taking better weapon proficiency with a Feat). The only thing a Cleric can't deal with by level 7 is lockpicking, and the game allows the option to smash locked doors and containers. This will cause some items in locked chest to be broken, and deny a stealthy approach, but when you're a combat monster already, stealth is overrated.
- Lockpicking isn't even specifically denied to them. A Cleric is only limited to how high they can raise the skill, but this is irrelevant since, with only a point in the skill, Clerics can open almost every chest in the game with skill and attribute buffs included since you automatically roll a 20 when picking locks out of combat. The only thing a Cleric truly cannot do is detect epic level traps, which requires a Rogue class feat. However, since traps pose no threat to a Cleric, this is not really an issue.
- The original Neverwinter Nights was even worse, with most essential cleric buffs lasting hours instead of minutes per level and spells such as Harm and Heal being more then capable of instantly-killing living and undead enemies respectively. Only after the expansions were introduced did clerics become more balanced, but if a vanilla server has a level cap under thirty, the best build will always be some kind of cleric unless nerfs are involved.
Guild Wars has the bizarre "55" builds. Using a specific set of items, the character incurs multiple penalties to his maximum HP until it drops to the lowest possible for a maximum level character—55. The character then uses a buff that prevents any single hit from dealing more than 10% of his health bar in damage—meaning all attacks drop to 5 damage or less. This is combined with health regeneration skills, skills that generate energy when struck, and a debuff that causes damage on a foe when attacking. The end result is a nigh-indestructible character that is laughably fragile if enemies just leave it alone for a moment.