Solomon Muto first appeared in the original series of Yu-Gi-Oh! He owns a game shop and he's the grandfather of Yugi Muto. Solomon Muto is the one who gave the Millennium Necklace to Yugi Muto. He also made several appearances in Yu-Gi-Oh! GX.
Slifer the Sky Dragon's name is completely irrelevant to the plot. It has no actual relation to the Egyptian God Osiris, it's just named after it. It's not like he's the only God in the Dub that isn't named after an Egyptian god anyway, since Obelisk isn't in either language.
Well coming next month or so they are adding the legendary exodia incarnate to the game so if they were to add Solomon at the time of the announcement for that card would be a good time, you know like you have to beat Solomon to be able to achieve the card or something like that lol I already know it's not though they're gonna do something with Yugi at level 50+ to be able to get the card
And he received a new one for his lines in Bonds Beyond Time and Dark Side of Dimensions. I doubt either of Maddie's major characters (the other being GX's Sartorius) are out of the running. The only thing that makes me question Solomon is Yugi having an Exodia skill already.