Well, Fallen Empires really doesn't have one main storyline, so maybe a collage made from the empire destroyers:
Farrel's Zealot,
Homarid Warrior,
Thrull Champion,
Orcish Captain and
Thallid Devourer, maybe?
Let's have a look here...
We might start with draft of Alpha/Beta/Unlimited -- that could be called "The Original Winner". The picture could be of
Black Lotus.
For Arabian Nights, "The Storyteller". The picture is
Shahrazad.
Antiquities -- I'd suggest shortening the title to "The Sylex Operator" with
Golgothian Sylex as picture.
Legends -- I'd suggest "The Legendary Hero". Hard to say who is the best "face" of Legends.
Adun Oakenshield looks quite heroic.
The Dark -- "The
Witch Hunter" would work. I think you need to keep these a bit similar, so for example they would all start with "The" and they would all be some sort of description that can be attached to a person.
Witch Hunter is a good picture to use.
Fallen Empires, how about "The Empire Vanquisher"? With the collage I've mentioned before.
Now Ice Age/Alliances. How about "The Frozen One"? A nice picture to use would be
Karplusan Giant.
Homelands, well, Unicorn Gourmet Chef is too specific for a single card. How about "The Home Invader"?
Chandler looks like he would fit the bill.
Mirage block: "The Unphased". A picture to fit would be
Spatial Binding.
Tempest block: "The Architect of Rath" was actually Yawgmoth, I'd guess. Maybe "The Ultimate Evincar"? While
Volrath didn't get a card in this block, there are some cards that depict him, for example
Fevered Convulsions.
Urza's block: This block is all over the place, locationwise, but it might be the best to take something from blue. I'd call the achievement "The Biographer of
Urza" and used the picture from
Catalog.
Masques block: This block was also strange, story-wise, as each of the three sets happened on different plane, and all happened roughly at the same time. But Rebels were in the whole block, so I'd call the achievement "The Leader of Rebellion" and used picture of
Cho-Manno, Revolutionary.
Invasion block: "Space Invader" doesn't fit much. "The Planar Invader", how about that? And the poster child is, of course,
Tsabo Tavoc.
Oddysey block: "The Threshold of Madness" is not really a title for a person, but maybe we can use Chainer's picture and give the title "The Dementia Master".
Onslaught block: Morph was one of parts of this block, but not really the main thing. That was tribal theme. I'd suggest "The Chief of the Tribe". The picture of
Voice of the Woods would fit.
Mirrodin block: I don't think they used the term "Mirran" back then, but "The Ravager of Mirrodin" would sound at least as good. But I kinda think it would be nice if the title pointed at the "main" expansion, and
Arcbound Ravager is from Darksteel (maybe there could be actually different achievements for whether you play with one, two or three sets?). So maybe, for Mirrodin, "The Connoisseur of Metal" with picture of
Gilded Lotus, to mirror the Unlimited achievement.
Kamigawa block: with the Japanese theme, I'd simply call it "The Shogun". For picture, I'd suggest Takeno.
Ravnica block: "The Guildmaster" is perfect

But which of the guildmasters to use? From the four in Ravnica I'd guess Szadek would be the best.
Coldsnap: You didn't mention this one, but Coldsnap was its own draft environment. The title might be "The Lord of Ice", with picture of
Heidar, Rimewind Master.
Time Spiral block: I'd suggest "The Temporal Archmage", Teferi's new moniker in Commander 2014, but picture of
Teferi, Mage of Zhalfir. After all, why not give him a title from another time?
Lorwyn block: It was a tribal block and important part of that were the changelings. "The Tribe Uniter" with picture of
Mirror Entity.
Shadowmoor block: The block was about color and it actually did contain a five-colored card. "The Pumpkin King" with picture of
Reaper King.
Alara block: "
The Maelstrom Conqueror" with picture of
Child of Alara would be fun, but I wanted something from Shards of Alara. If colors are unequal, my default color to go is blue (as it best represents the player), so maybe "The Shard Conqueror" with picture of
Sharding Sphinx.
Zendikar/Worldwake: "The Intrepid Explorer".
Cliff Threader would be a nice picture.
Rise of the Eldrazi: "
Leveler" doesn't really work as a title. Perhaps "The Experienced Explorer". A leveler that would fit that description might be
Skywatcher Adept.
Scars of Mirrodin block: "The Metal Overlord". Picture would be of
Platinum Emperion.
Innistrad/Dark Ascension: "The Monster Hunter". Picture of
Elite Inquisitor.
Avacyn Restored: "The Restorer of Avacyn" with
Avacyn, Angel of Hope.
Return to Ravnica block: This is a complex one since each of the set had different draft environment. This at least requires an achievement for every set.
RTR/RTR/RTR draft: "The Genius of Guilds" with
Niv-Mizzet, Dracogenius.
GTC/GTC/GTC draft: "The Crasher of the Gates" with
Aurelia, the Warleader.
DGM/GTC/RTR draft: "The Runner of the Maze" with
Exava, Rakdos Blood Witch.
Theros block: "The Classical Hero" with
Fabled Hero.
Khans of Tarkir/Fate Reforged: "The Clan Leader" with
Surrak Dragonclaw.