Definitely Meg Griffin from Family Guy. Maybe it's because I'm constantly getting told I look just like her, but I don't completely understand why she gets so much abuse on that show.
Milhouse Van Houten from The Simpsons. I think if I were a Simpsons character, I'd be him and I feel bad that he loves Lisa so much and cares about her a lot but rarely gets her attention.
Klaus on American Dad! He's always getting ignored and disrespected and he's actually one of the funniest and smartest characters on the show, in my opinion.
Also, Martha Jones on Doctor Who. Mainly because she seems to get a lot of hate in the fandom and I personally loved her as a companion. She was brilliant, I think
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"Have you never seen something so mad, so extraordinary... That just for one second, you think that there might be more out there?" -Gwen Cooper, Torchwood