Looking for an episode to watch tonight in Walter's honor. I know he was relatively a side character in TOS but I'm open to any suggestions!

Not an episode but ST IV for "wessels" comes to mind

I thought about that, it's probably Chekov's finest appearance but I just watched it recently!

Koenig said one of his favorite episode was “Spectre of the Gun”.

whats scary was he was the young guy. the ensign. several episodes he is infatuated with girls. like the ok corral one.

The Starlost - The Alien Oro

I was just reading that, I think thats the one!

Right? There's a line in Generations where Kirk tells him "you were younger" than a new ensign.

The Psi Corps is Mother, The Psi Corps is Father.

I opted for "The Tholian web", and it opens on Chekov. Maybe he's not super prominent in it otherwise, but it's a peak TOS episode.

Edit: Watching it now, he has some good away team scenes, and that great freakout on the bridge when Kirk's fate is uncertain. Definitely a Koenig showcase!

In Gamesters of Triskelion he's featured rather prominently. Mirror, Mirror is a great one because he gets to really cut loose.

Ohh yes both good suggestions thanks