Goodman Games

There was this NPC, the Cat Lord. He appeared in Monster Manual II for AD&D1 and Epic Level Handbook. Quite a character.

Recently I was practicing monster creation/conversion in D&D4 and got an idea of a short adventure about the Cat Lord. I wonder if it's worth it to make it into a pdf and distribute as free supplement. So, I need an advice:
1. Is Cat Lord copyrighted? If he is, what if I make a similar cat-themed character? How much similarities can there be?
2. Do I use GSL like OGL or I can even use OGL? Are there differences in usage?

Thanks %)

IIRC Cat Lord appears in the Tome of Horrors 1, from Necromancer Games, so you should be able to use him as a 3.x/d20/OGL monster no problem.

1) The specific text of the cat lord from MM2 AD&D1, Epic Level Handbook, and the Tome of Horrors 1 is copyrighted. OGL allows you to reuse the Tome of Horrors 1 version. You can certainly make a similar cat-themed character. How much similarity is allowed is up to debate.
2) GSL is very different from the OGL. You download them and read them. The GSL needs to be signed and sent to WotC. Game mechanics cannot be copyrighted but specific text describing them can. It is possible to create a 4E compatible product without the GSL. Goodman games did that initially. WotC said they were going to have a fan site policy but have never created it. For a free pdf I probably would just make sure the creature is distinct from the Cat Lord and just put it on my web site.