Or, rather, the sacrificial mouse.
Some fanart for The Secret of NIMH. God, I remember seeing this movie whilst flicking through channels when I was 7. It was right in the middle where Mrs Brisby was reading about how her husband, Jonathan, died though and I had no idea what the hell was going on. It was about a year or so later before I watched it (and the sequel) in full.
I know many people have Justin or Mrs Brisby herself as their favourite character but, funnily enough, my favourite character has always been the enigmatic Jonathan. The poor guy is spoken about with so much respect by so many creatures in both the book and the film (by an owl and a bunch of rats, no less) and yet we know very little about him. Initially, from watching the film, you assume Jonathan is merely famous because he alone had the ability to open a door that allowed him and his companions to escape from a cruel laboratory but it's clear he's well-liked for other reasons as well. I like to think he was just a brave, likeable guy who wasn't afraid to put himself before his friends. Sneaking into a human's kitchen and drugging a dangerous cat was obviously second nature to him, despite having a family at home. There's also the whole question of how an owl, a natural enemy of mice, came to respect him in the first place.
In short, regardless of how little we know about him, Jonathan was a badass.
Here, he's arriving at the conclusion that, despite the entrance to the Fitzgibbon kitchen being too large for a rat, it's just the right size for a mouse. Thus, he becomes the official go-to guy when it comes to drugging Dragon. Unfortunately, his luck runs out one night and, as we know, he is killed.
You can see I've drawn him using eyeglasses. The exact details of his death aren't known except that he was evidently killed by Dragon but my theory is that Jonathan had failing eyesight and simply could not work his way back to safety without his glasses. It's a bit of a strange theory but I'd like to think the experimentation at NIMH had some nasty side effects for the rats/mice that would cause some kind of disability (i.e. hearing loss, lack of eyesight).
Also, he's wearing Mrs Brisby's cape. Now, many people in the NIMH fandom do draw Jonathan in a similar attire to Justin and green is often a colour assigned to him (probably to contrast with Mrs Brisby's red cape) but here I've just gone with red. That red cape had to come from somewhere and, of course, my theory is that it originally belonged to Jonathan. Obviously, as his loving wife, Mrs Brisby will have held onto something belonging to her late husband. He was originally going to have a separate green cape of his own but, like I said, his attire is often coloured green so I decided to go with red. Just to be different. lol
The background is just a still from the movie. This was meant to be just a quick doodle of Jonathan and, yeah, backgrounds take effort, man.