I used to avoid Leo for the most part, mainly because of its popularity. I did like the meaning and the pronunciation, there was nothing bad about the name apart from its rank on the popularity charts. Along with other -o ending names, Leo would fit brilliantly among my other names. It does feel incomplete to me.
I like Leon & Leopold the best. I was wondering if there are any other full names that can have Leo as a nickname.
TIA
[name_f]Leonine[/name_f]
[name_u]Leland[/name_u]
[name_u]Leander[/name_u]
[name_m]Lion[/name_m]
[name_u]Elliott[/name_u]
[name_m]Elio[/name_m]
leonard
leonardo
leone
leander
leandro
[name_m]Leonidas[/name_m] and [name_m]Leolin[/name_m] are some of my favourite options for [name_u]Leo[/name_u]. [name_m]Leolin[/name_m] especially doesn’t come up much.
Of the ‘lio’ endings I particularly like [name_m]Bráulio[/name_m], (great meaning) [name_m]Celio[/name_m] and [name_m]Tulio[/name_m].
[name_m]Leonce[/name_m] 
[name_m]Leonidas[/name_m] is a favorite, beyond [name_u]Leon[/name_u] and [name_m]Leopold[/name_m]! I think [name_u]Elliot[/name_u] nn [name_u]Leo[/name_u] is sweet too, though Elliot’s not much more rare than [name_u]Leo[/name_u] is…
[name_u]Elliot[/name_u]
[name_m]Napoleon[/name_m]
Appellation Mountain did a great list on Leo names: Leo Names: From Leonard to Leovanni - Appellation Mountain
@Victory55 [name_f]Leonine[/name_f] and [name_u]Leander[/name_u] are amazing.
@alessia810 I have never heard of [name_m]Leandro[/name_m] before. I love the -o ending that follows here.
@EdgeOfTheMeadow I like [name_m]Leolin[/name_m] & [name_m]Leonidas[/name_m]. Should’ve thought of -lio ending names before. [name_m]Celio[/name_m] has a great meaning!
@Greyblue [name_m]Leonce[/name_m], at first sight, is a beautiful name. I just can’t help but think of ‘seance’ lol.
@ashthedreamer [name_m]Leonidas[/name_m] has to be my favourite among all the suggestions.
@shanade213 [name_m]Napoleon[/name_m] is an incredible name, but with certain weight to it.
@CarolAnn The link was very helpful. Thank you. [name_f]My[/name_f] favourites from there are [name_m]Leonel[/name_m], [name_m]Leoncio[/name_m], [name_m]Leofric[/name_m] and Leomar!
Thank you! 
[name_m]Leonides[/name_m]
Leo…
[name_m]Leonard[/name_m]
-Leonardo
-Leon
[name_m]Just[/name_m] [name_u]Leo[/name_u] maybe would be cute 
[name_m]Galileo[/name_m]
[name_m]Leonidas[/name_m]
[name_u]Lionel[/name_u]
[name_u]Elliott[/name_u] (maybe a bit of a stretch?)
[name_u]Lennon[/name_u]
[name_u]Leander[/name_u]
[name_u]Elias[/name_u]
my favs are leon and leonidas 
some others:
leonilo
leonid
leonides
leonel
leomar
leomaris
leofric
leocadio
leopoldo
lionel
leander
leandro
lennon
lennox
leland
eleodoro