Argus, The Golden Businessman
(This is completely open to suggestions) Argus is a late-game mage that utilizes gold as his resource, "investing" it into damage before receiving a higher payout.
Lore Argus is the head and creator of Hextech Co., a thriving research facility in Piltover that, along with being partially responsible for Piltover's prosperity, has dubious connections to Zaun's Viktor. He originally invested into several research projects throughout both Piltover and Zaun, turning over a hefty profit as they began to thrive. Argus, while not necessarily agreeing with the whole "glorious evolution" thing, found Viktor's research in Hextech and human enhancement promising, and offered his assistance by creating Hextech Co. Though under the Piltover Police and Jayce's surveillance, they've yet to find solid evidence that connects Argus to Zaun's less-than ethical projects.
Abilities
Passive: Investment - Argus puts an "Investment" stack, giving 1.2 gold for every 1 gold spent damaging unit on its death(1.4 gold on champions & large monsters). He also gets +5 gold per second, increasing by 1 for every level past 1.
Q: Money Shot - 6/7/8/9/10 gold(+5/5/6/6/7% current gold) - Argus shoots a golden bullet from his Hextech gun(targeted), dealing 17/24/31/38/45(+80% AP)(+100% gold spent) magic damage.
W: Guards/Arrest - 2% current gold, 10% on summon - Argus rings up two bodyguards that last 6/7/8/9/10 seconds, have 75/90/105/120/135(+32/44/56/68/90% gold spent) health and attack units that damage Argus, dealing 10/25/40/55/70(+10% AP) physical damage. Activating the skill again(skillshot) will send a guard out to grapple the first champion it catches, dealing damage and snaring the opponent for 1.2/1.4/1.6/1.8/2 seconds before returning. At max level, the guard stuns.
E: Midas Touch - 30/27/24/21/18% current gold - After a short delay, Argus shoots out a glob of gold that coats target unit in gold(stasis) for 2 seconds. If the unit is an enemy, Argus deals magic damage equal to 30% of gold spent(+20% AP).
R: Make it Rain - Initial cost of 20% current gold, 10/9/8 gold per second, toggled - A chart arrow appears above Argus' head, and he gains "Make it Rain" stacks equal to 50% of gold spent. For every second Make it Rain is active, Argus gains stacks equal to the amount of gold lost per second, and the cost to keep Make it Rain active goes up by 3/4/5 gold. When the skill is deactivated(manually or by lack of funds), Argus deals damage in a large area around him equal to the number of Make it Rain stacks(+50% AP).