Most popular male MLP character.

Who’s the most popular male MLP character?

Spike (Twi’s boyfriend), Big Macintosh (AJ’s bro and Sugar’s husbando), Discord (Fluttershy’s bf), Shining Armor (Twi’s bro and Cadance’s husbando), King Sombra (ded king), Gallus (tamed carnivore).
 
I see them often than any other males.
 
Secondary (saw them less often than the former but still often)  
Sandbar, Button Mash, Rumble, Quibble Pants, Zephyr, Bulk, Cheese Sandwich
 
Rarely seen But I remember them, I guess not popular enough:  
Ahuizotl (Daring Do’s boyfriend), Dr Cabal (Daring Do’s 2nd boyfriend), Seabreeze, Storm King

@Background Pony #0051  
Some more rarely seen: Tirek, Rockhoof, Flash Magnus, Starswirl…

@Background Pony #0051  
Some more Secondary: Sunburst (Glimmy’s boyfriend), Thunderlane, Soarin’, Night Light (Twidad), Bright Mac (Appledad)
 
Rarely seen: Neighsay, Iron Will, Firelight (Glimdad), The rest of the dads

Probably Big Mac or Spike

Id say Spike, Discord, Big Mac, Sombra all have a lot of art fanfics and fanmade music and such created of them.

Outside the fandom I’d say Discord because of the Discord app, I’ve seen quite a few people come across that living tombstone remix because of this.
 
Inside the fandom probably Spike, he’s in most episodes, is there since the first episode all the way to the end, and he’s even in g1.
 
That being said this is all assuming you mean popular as in how well known they are, and not how well liekd they are.

@TheGlitchedWolf  
Discord definitely well liked alot outside of the fandom interestingly he seems to have better reception from non bronies who say they don’t really like mlp as a whole but think discord is the best character.

Probably Big Macintosh