So, uh, making RPG characters is actually kind of a hobby of mine. I've got a handful of them done up for a variety of systems, with varying degrees of backstory detail (leaving that open makes it easier to adapt them to the campaign after all). I chose this one in particular because 5E is quite simplistic in terms of character creation compared to most, and because Wizard is the class that I feel represents me best. Ability scores are generated using the default point-buy method.
Forest Gnome Wizard/Rogue
Background: Guild Artisan
Proficiencies: Wizard weapons, (Light Armor), (Rogue Weapons), Alchemist's Lab, (Thieves' Tools)
Skills: Insight, Persuasion, Arcana, Investigation, (Perception)
Saving Throws: Intelligence, Wisdom
Languages: Common, Gnomish, Draconic, (Thieves' Cant)
1st level Wizard, 2nd level Rogue, 3rd-20th level Wizard
(Brackets indicate something learned from Rogue multiclass).
Expertise Skills from Rogue: Investigation, Perception.
Specialty School: Illusion.
5th-level: Feat (Tough).
9th-level: Feat (Linguist).
13th-level: Feat (Observant - ability score point in INT).
17th-level: Feat (Keen Mind).
20th-level: +2 DEX.
This character is meant to be a resourceful kind of caster, the type who tries to have a solution to the miscellaneous obstacles that bar the party's progress in ways the other members might not be well-equipped to deal with. In practice, much like a bard, but operating off of guile and discretion rather than flair. I don't have any roleplaying info done on any of my 5E premades, so this is more of a "character plan" than an actual full-fledged character, but I often have trouble coming up with those details without a world and a party for the character to exist in.
I didn't detail all the class abilities that would be unlocked, because that would make this incredibly long and tedious, but I did lay out any mechanical choices that would have to be made.