Tony Markovich is the neighbor and Police Officer, who bore a liking for Fiona for some time. He initially lives with his over-bearing mother, whom he's desperate to impress.
History
Season 1
The Gallaghers attempt to keep Tony sweet in order to keep out of trouble, however as Tony gets more involved in their lives when he begins dating Fiona. Tony lost his virginity to Fiona but things are awkward between them and he invites her to dinner. However, he grows more cautious of Steve's illegal activity, resulting in a vendetta that has him arrest Steve once catching him in the act.
Tony attacks Steve and gives him the option to turn himself in or disappear lands Lip and Ian under arrest.
Season 2
In Can I Have a Mother Tony is re-doing his house, having found a new girlfriend (who may or may not be purchased from the internet, as stated by Jimmy). He is not pleased to see Jimmy again but begrudgingly accepts his bribe of making amends.
Later on, he stops the arriving police from arresting Fiona's grandmother Peggy Gallagher
Season 3
During Where There's a Will, he nearly carries out the eviction notice of the Gallaghers after they attempted to kill their antagonistic cousin Patrick Gallagher who wanted them out the house. However, Debbie lies that Patrick made advances on her and Tony almost arrests him. For this, Patrick questions if Tony was on his clearly lying relatives' side but Tony states he wants justices. Tony releases Patrick once Fiona makes an arrangement and the family keep the house.
Season 4
During Simple Pleasures, he and his fellow cops do a bust on a house where they find a passed out Frank. Tony is exasperated, as he is well aware of Frank and tells his partners, he's got this. He brings Frank back to his house and finds Carl there. Tony asks where Fiona is, as Carl tells him that she’s with some guy named Mike Pratt at a game. Tony is pleased to hear Fiona moved on and Carl good luck with his father before he leaves the house.
Season 6
In Refugees, Tony shows up at a baseball game as a member of an all-gay team of police officers. At the game, he greets Fiona's brother Ian who is surprised to see him and they share a hug. Ian then asks him when he came out, and he jokes that Fiona turned him gay.