Bellerophon was a hero, who found Pegasus and used it as his mount. In SMITE, he is a very aggressive warrior while on Pegasus, and has some utility while off of his mount. Overall, he is very strong in duels, and pretty good in teamfights. He is depicted as such:

(Obviously, this is not my artwork, just what I thought he would look like.)
(Also, if you are familiar with League of Legends champions, his passive is similar to Kled's.)

Difficulty: Hard
Attack Progression -
On Pegasus: 1x/1x/1.5x, the last attack dealing damage in an AOE around him
Off Pegasus: .5x/1x/.5x

Passive - Pegasus

Bellerophon rides his mount Pegasus, who changes his abilities and grants him movement speed. When Bellerophon drops below 30% health, Pegasus flies away, forcing Bellerophon to fight on the ground and use his sword. While without Pegasus, his abilities change and he gains increased attack speed. When his health goes above 60% while in unmounted form, Pegasus flies back to aid Bellerophon again, changing him back to mounted form.

Mounted form movement speed: 5% +.5% per level
Unmounted form attack speed: 10% +1% per level

Ability 1 - Spear Slash/Bladework

While mounted, Bellerophon slashes three times consecutively in a cone in front of him, dealing damage each strike. If he hits an enemy with all three strikes, they become slowed for a duration.
While unmounted, Bellerophon strikes with his sword, dealing damage in a line in front of him, then dashes a short distance in the direction he's moving (Much like Rama's or Thoth's dashes). This ability applies on-hit effects.

Mana cost (mounted and unmounted): 55/60/65/70/75
Mounted -
Slash damage: 30/50/70/90/110 (35% of physical power) per slash
Slow strength: 40%
Slow duration: 2 seconds
Cooldown: 10 seconds
Unmounted -
Thrust damage: 70/130/190/250/310 (50% of physical power)
Cooldown: 6 seconds

Ability 2 - Rallying Shout/Unnatural Strength

While mounted, Bellerophon shouts to his allies for assistance, granting an aura that increases the power of nearby allies and himself for a duration. For each ally nearby, Bellerophon gains protections.
While unmounted, Bellerophon becomes stronger, granting his next 3 successful auto attacks extra true damage and healing.

Mounted -
Mana cost: 60/65/70/75/80
Aura duration: 6 seconds
Power buff: 10/20/30/40/50
Protections: 3/4/5/6/7 per each nearby allied god
Cooldown: 16 seconds
Unmounted -
Mana cost: 40/45/50/55/60
Extra true damage: 15/25/35/45/55 (10% of physical power)
Healing: 20/30/40/50/60 (30% of physical power)
Cooldown: 10 seconds

Ability 3 - Trample/Parry Strike

While mounted, Pegasus charges, gaining movement speed, removing unit collision, and dealing damage to enemies Bellerophon passes through. Casting Spear Slash while charging will end the ability (putting it on cooldown and deal extra damage on each of the slashes.
While unmounted, Bellerophon prepares for an enemy attack, becoming CC immune for a short duration. If he is hit by an ability while CC immune, he deflects the ability and stuns the caster for a duration. While they are stunned, Bellerophon can activate the ability again to dash to the stunned target, dealing damage to the target.

Mounted -
Mana cost: 65
Movement speed: 10/15/20/25/30%
Duration: 5 seconds
Pass through damage: 60/100/140/180/220 (50% of physical power)
Spear Slash extra damage: 30/50/70/90/110 (20% of physical power)
Cooldown: 16 seconds
Unmounted -
Mana cost: 80
CC immune duration: .75 seconds
Stun duration: 1/1.2/1.4/1.6/1.8 seconds
Dash damage: 80/130/180/230/280 (40% of physical power)
Cooldown: 23 seconds

Ultimate - Steed of Legend

Passively, Bellerophon gains protections equal to a percentage of his movement speed while on Pegasus. Actively while mounted, Bellerophon dares nearby enemies to challenge him and Pegasus, taunting all enemy gods nearby and granting Bellerophon damage reduction for a duration. He cannot cast this if he is unmounted. He loses the protections from his passive while his ultimate is on cooldown.

Passive protections: 10/20/30/40/50% of movement speed
Mana cost: 100
Taunt duration: 1/1.4/1.8/2.2/2.6 seconds
Damage reduction duration: 2/2.5/3/3.5/4 seconds
Damage reduction: 30/35/40/45/50%
Cooldown: 90 seconds

Hope you like the concept!