For my Eponymous PC I've had a lot of multiclassing.
He started out in 2e as a myrmidon kit human (viking type) fighter who traveled switched class to mage and eventually learned 1e OA martial arts.
In 3e He got converted to 7th level for a Banewarrens game with 2 PCs. IIRC I went with Ranger 1, Monk 1, Wiz 5, variant of harper mage from Magic of Faerun 3, and then loremaster. So 4 classes by level 10 and 5 by level 11.
When we converted to 3.5 he went eldritch knight to get closer to the viking warrior roots and so his sword wielding was actually competent instead of merely ineffectually there. I also dropped monk for just Improved unarmed strike and acquired my own deflect arrows gloves, ring of evasion, and monk's belt to keep the tertiary martial arts skills flavor. So in 3.5 he is (in one game currently) a rgr 1, wiz 5, harper mage 1, eldritch knight 9, abjurant champion 1 (had the DM gotten CM earlier I would be higher in that class) at 17th level.
Now most of my characters stick with one or two classes, but this one had a lot of history and can best be done through multiclassing (he's been used in a bunch of different games with different iterations, UA variant barbarian instead of the ranger, gestalt ranger wizard, Everquest RPG rogue and ranger, straight wizard with weapon proficiency heading towards loremaster, and ranger wizard, and a Vampire the Masquerade NPC spellcasting hunter by another DM).
In 4e I expect he'd be a wizard with multiclass feats for a melee striker class.