Most character types are pretty setting-specific.
Fighter pilots need settings with fighters, classical wizards need settings with studious magic, hackers need computers, swordsmen need melee opponents (and, preferably, a game system which makes it possible for them to fight a lot without winding up crippled or dead), fey selkies need settings with seas and the lands of faerie, priests who tap into their gods powers need powerful gods.
Incompetent and ineffectual idiots fit in anywhere – but they aren’t much fun to play.
There’s only one type of character that finds a place in pretty much every world.
The Expert. Master of a particular set of skills or – in settings which feature other sources of power – of an immense array of skills.
Experts can be accommodated in almost any game. They don’t require any particular race, or setting, or power source. They can satisfy pretty much any desire for realism. They’re often very handy to have along. There are a lot of good reasons to play experts.
On the other hand, they’re dull, simply because they are somewhat realistic. They won’t have any spectacular special abilities to show off or attract the players who want some escapism beyond “you’re unreasonably good at a lot of things, rather than simply being vaguely familiar with them like most people”. When it comes to power-based combat, magical manipulations, using psychic abilities, or superheroics, the Expert won’t have much to do.
Experts are also the only character type where EVERY other character in the group will automatically be stepping on their role. The telekinetic handles the telekinesis, Mr Smash handles the super-strength, and the martial artist handles the mystic chi powers, without competition. No party understudy is ever going to match a power-specialist in any situation, although they may find other ways to handle situations.
But every other character is going to have some skills. If the skill in question is related to their speciality, or is a particular hobby, they may be just as good at it as the Expert. That’s one of the major reasons why quite a lot of adventuring groups manage to get along without an Expert at all.
To really have a role in groups where power sources other than skills are available, an Expert needs to be impressively competent – good enough that, even in their specialities, other characters will not be a match for him or her when it comes to skills. They also need to be good at a wide range of skills; otherwise they’ll often have nothing to do.
That chips away at the “believability” factor of course, but there’s always a price to pay somewhere. Game design, just like any branch of engineering, is always the art of tradeoffs.
So: to be playable, a dedicated Expert needs to have more skills than anyone else – and needs some way to be a lot better at them than anyone else.
Ergo, they’ll need some special abilities when it comes to skills. They’ll have to be able to acquire them more easily than other characters and to have them at higher levels than the other characters. To go any further, we’ll need to pick a game system to use as an example.
Since I’ve built the necessary elements into Eclipse: The Codex Persona d20, I’ll use that one.
What will you want to buy in Eclipse to be a serious Expert?
Fast Learner, Specialized in Skills to increase it’s effect – for an extra two skill points per level. (6 CP).
Adept, to half the cost of four of your favorite skills. (6 CP). If possible, you’ll want to get it twice. If not, you’ll want to specialize it to let it cover eight skills. Unfortunately, specializing Adept – which is already limited to specific skills – is a bit difficult. I have let people get away with “must return to the great library and study there” to stretch Adept to cover eight knowledge skills, or even “must locate expert trainers and persuade them to teach you to take advantage of the price break”.
To be really good at skills in a particular area – Dexterity-based skills, Charisma-based skills, or some such – you can buy Augmented Bonus (Adds Intelligence Modifier to the relevant attribute modifier for skill purposes, 6 CP). You’ll want to pick a speciality, since you can’t afford too many special abilities at first level – but in that speciality you’ll be very very good compared to anyone else.
If you think you can afford it, you might want to take Augmented Bonus to add a second attribute modifier to your intelligence modifier for the purposes of calculating skill points per level. That costs 18 CP however – which is quite a chunk of the basic 48 CP available at level one. It will pay some fairly impressive dividends later on however.
Later on an expert will want to pick up some Innate Enchantment – picking up enhancements to especially-important skills – as well as abilities like Skill Focus and Skill Emphasis, or even Immunities to the normal limitations of skills – allowing them to use their skills to do things normally impossible.
Some combination of those abilities, even if a starting character can’t afford all of them, will make for a pretty impressive Expert.
It will help that – with skills like Martial Arts and Rune Magic available – an Expert can have some combat and magical (or psychic) tricks on tap for use in situations where simple skills are not enough. That won’t make an Expert a match for a dedicated mage, warrior or other specialist – but it will help make sure that they’ve got something to do.