Milton Waddams. Even when he wins, he loses. He said no salt on that margarita 
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Jeffery “The Dude” Lebowski. The movie wasn’t even named after him, but heck, the Dude abides.
Ralph Kramden and Barney Fife are my favorite classic TV losers. Sid Caesar, in Your Show of Shows played a hilarious loser in many of his Your Show of Shows sketches. Although the character of Frasier Crane in Frasier was refined and successful, Kelsey Grammer nailed the butt-of-the-joke loser in most episodes. From the silent era of movies, my favorite hapless loser was the typical Harold Lloyd character:
I’d say Jar Jar Binks. The guy was detested and cringeworthy, but he honestly had a good heart and was trying to do his best despite his many built-in mental flaws.
You realize he was a secret Sith Lord right? All of the "Meeza"s was an act.
Ted Buckland, from the sitcom Scrubs, played brilliantly by Sam Lloyd.
Garry (Jerry? Terry? Larry?) on Parks and Recreations at work, although his home life is ironically magnificent.
Good one. I was going to mention Phil, but I like him so much and felt bad calling him a loser 
Oh! Mentioning Phil makes me think of Needle-nose Ned! We didn’t get to know him very well, but he probably fits this category.
Frank Burns! Detested by all and the butt of many jokes. I was never so happy as when Houlihan finally broke up with him.
Topher Grace has made a career out of playing a milquetoast, Charlie Brown-esque archetype. On That 70’s Show and on Home Economics he’s basically played the same character. And of course, he reprised the role of Eric Forman for That 90’s Show, and the character has not developed at all. Still the same timid, nerdy, nebbish.
Richard Hendricks of Silicon Valley.
George Costanza, Frank Burns, Topher, even Richard Hendricks all seem like characters hoisted by their own petards; not hapless.
George McFly. He did win out in the end, but he was the butt of all jokes for most of the movie. He cleaned up pretty good-looking for the dance, though.
Tobias Funke and Buster Bluth.
Does Philip J. Fry from Futurama count?
If not I pick Jerry Smith from Rick and Morty
Yeah… I hesitated to call him a loser. He is, partly so. When I see him though, I can’t help but think of Major Frank Burns, at least partly so.
It’s not just his characters, he’s a hapless loser as an actor. He ditched That 70’s show before it ended because he didn’t want to be considered a child actor anymore. He cut his personal ties with the other actors on the show, and then failed terribly at playing serious roles. Finally he returned to Home Economics to play the Eric Forman character again, apparently the only role he’s good at. Hope he chokes every time he sees Mila Kunis and Ashton Kutcher show off how rich and successful they are.
I know a guy in real life who constantly has tragic things happening to him. He’s a little fella (5’6", maybe 130 pounds) and he has a small farm. He once got trampled by a bull. It looked like a mugger beat the crap out of him. Another time he was up in the hayloft of his barn. He misstepped and fell from a height, breaking a leg.
His wife was cheating on him. When he found out and confronted her, she said she wanted a divorce. Before he could file, she cleaned out their joint accounts and took off, never to be heard from again.
He also used to drive an 18 wheeler. During a storm he had to climb on top of his load and the wind blew him off. Again, horribly bruised and battered.
He unknowingly used cocaine for years. He got it from another trucker, who introduced him to it as “nose candy”. One day when I asked him about staying awake for long trips, he mentioned nose candy helping. I was shocked; he’s a little farmer dude! When I mentioned cocaine, he was shocked. He said hell no, he doesn’t use cocaine, just nose candy.
He eventually lost his truck. He was injured and his nephew helped him out by driving for him. The kid took an exit too fast and rolled the truck over onto its side. Nose candy was involved. It was determined definitively then by the police that nose candy = cocaine.
Bob Wheeler & Family from Night Court.