Yellow Zelkova is a bulky Metarex commander with a deep green visor, bulky yellow armor and matching green orbs on his head. His cape which denotes his position as a Commander of the Metarex, is green. Zelkova's height seems to change throughout the anime. At one point, he is about that same size as other Metarex, and would be about twice Sonic the Hedgehog's height. However, in his final fight against Knuckles the Echidna, his foot is large enough to crush Knuckles and hide him from view.
When Zelkova's armor is destroyed, he is revealed to have lime skin, pear-colored hair with yellow horn-like growths and wore an orange long-sleeved shirt with a darker outline along the edge, two yellow strips on each sleeve, and is held by an emerald stone.
Many years ago, Yellow Zelkova was originally an alien who had decided to follow Lucas and his followers in staying behind on their planet to fight. Despite the power they had obtained in their monster forms, they met the opposition with much failure. Eventually Lucas came up with a plan to transform their bodies into that of techno-organic machines. Yellow Zelkova and the others then took on new identities. Under the leadership of Lucas (now known as Dark Oak), Yellow Zelkova and the others eventually built and assembled an army of robots, referring to themselves as the Metarex.
Following Red Pine's death, Zelkova is discussing their fallen comrade's failed plans with the other two Commanders. Zelkova noted it was strange, that Red Pine was usually very careful with his plans. He announced to his subordinates to ready to leave on his command. Zelkova first engages Sonic and his friends when Dark Oak dispatches him to the Intergalactic Cloister to get rid of Sonic and his allies. He put up a good fight, but he proved too slow to defeat Sonic and Knuckles, the latter of whom he formed a rivalry with. He swore vengeance, vowing that the Metarex would destroy them. He later joined up with the other commanders to attack the Blue Typhoon, though he strongly disapproved of Dr. Eggman joining forces with them.
Zelkova later attacked the Blue Typhoon again, equipped with a special shield pack that blocked all of his enemies' attacks. However, his shield proved ineffective against Knuckles, who smashed Zelkova's knee. Sonic and the others then used collected lightning to overload Zelkova's generator, destroying his outer shell and revealing Zelkova's true form: that of a massive male specimen of Cosmo's species. Zelkova was then knocked into a nearby lava pit by Knuckles' punch. Knuckles jumped into the pit to try to save Zelkova, but Zelkova refused, slid into the lava and died.
Zelkova considers himself the (physically) strongest Metarex commander, and brute force is his answer to everything. He is an outrageous idiot and not the brightest in the bunch, considered an "invalid" by both Dark Oak and his comrades Black Narcissus and Pale Bayleaf. His gullible nature can be seen when he shows his shield pack made by Eggman, as after he finishes bragging about it, he adds "And that's not all! As a bonus, I get this free Eggman temporary tattoo!" (this line is only in the dub, not the original). Unlike most Metarex, he uses no weapons, relying on his fists and head to attack enemies, as well as anything that he can throw at his enemies.
Powers and abilities
Yellow Zelkova has far more physical strength than the other Metarex commanders, and his body is extremely well armored, though how strong his shell is a bit inconsistent. He is capable of lifting the massive pillars easily and throw them with formidable force, and even overwhelm Knuckles in combat (though Knuckles could defeat him later). In his debut, he could even survive a direct hit from the Sonic Power Cannon, but in his final battle with Knuckles, his outer shell was able to be destroyed.
- "You still have not learned, have you hedgehog?"
- —Yellow Zelkova whilst fighting against Sonic, "Zelkova Strikes Back".
- "Dark Oak will be victorious! He will have revenge!"
- —Zelkova shortly before falling into lava, "Zelkova Strikes Back".
- Yellow Zelkova was the first Metarex to survive a direct hit from the Sonic Power Cannon.
- Zelkova dies in a similar fashion to Hyper Metal Sonic's death in Sonic the Hedgehog: The Movie. However, the dub cuts the part just as Knuckles jumps in.
- Zelkova is a genus of several trees native to southern Europe and Asia. This signifies that the name "Yellow Zelkova" associates with plants like his other fellow Metarex commanders' names.