Charlie and Frank

Charlie Kelly and Frank Reynolds have become close friends and roommates since meeting at the beginning of. Frank was heavily suggested to be Charlie's biological father throughout the series until Charlie meets his father in The Gang's Still in Ireland.

Early History
Until Season 15, it was implied that Frank was Charlie's father, having had a one night stand with Charlie's Mom that resulted in a baby who couldn't be aborted. Charlie possibly knew Frank in passing as Dennis and Dee's father, but there is no confirmation of this.

Season One
Frank was not in season one, though Pop-Pop briefly tells Charlie, who he thinks is Dennis, of his "bastard father"- shockingly accurate due to the later reveal of Frank likely being Charlie's dad. ("The Gang Finds a Dead Guy")

Season Two
Frank moves in with Charlie and offers to help pay his rent. Frank having grown disillusioned with his rich yuppie lifestyle wants to live in squalor like he used to. Frank sleeps with the two strippers Mac and Charlie were planning to sleep with by locking them out of Charlie's apartment. (Charlie Gets Crippled)

Charlie teaches Frank the art of making a Grilled Charlie. (The Gang Goes Jihad)

Frank puts all of his money in Charlie's bank account to hide it from his wife Barbara Reynolds. Mac and Charlie spend the money on hookers. Frank is impressed with Charlie's guts and promotes him to manager. (Dennis and Dee Go on Welfare)

Frank sleeps with Charlie's crush the Waitress. (Mac Bangs Dennis' Mom)

Charlie's mother, Bonnie Kelly contacts Frank via Myspace. It is revealed that Bonnie and Frank slept together 30 years ago and that Frank may be Charlie's father. (Dennis and Dee Get a New Dad)

Season Three
Charlie and Frank become obsessed with trash, bringing everything they can find back to their apartment. Frank is adamant that he is not Charlie's father, because Charlie's mom had an abortion. He insists that Bonnie must have gotten pregnant after she "banged some dude" after the abortion. Charlie discovers that Bonnie had the abortion but Charlie survived. Bonnie says she had to keep it a secret from Frank because he was married to Barbara Reynolds at the time. If he had found out he would have made Bonnie throw him in a dumpster. Charlie then becomes convinced that the dumpster baby Dee and Mac found is really Frank and the Waitress' son even though they had only slept together 3 months earlier. The Waitress calls child protective services. (The Gang Finds a Dumpster Baby)

Frank laces Charlie's beer with LSD thus turning him into his alter ego Green Man. (The Gang Gets Invincible)

When the gang gets held hostage by the McPoyles Frank enlists Mac to make sure Charlie dies so he can't inherit his fortune. Charlie destroys the will. (The Gang Gets Held Hostage)

Frank and Charlie conduct their own investigation into whether or not Mac is a serial killer, with Frank breaking and entering, wanting to torture Mac with a chainsaw, and so on, while Charlie tries to be the lawyer and point out Frank's lack of evidence and such (Mac Is a Serial Killer).

Frank moves out of their apartment and moves in with Charlie's mom Bonnie Kelly, who becomes his new "bang maid" handing out massages and handjobs like hotcakes. Charlie is jealous of his mother stealing Frank away from him. He plots to make Bonnie fall in love with Mac's drug dealer father Luther Mac so he can have Frank back. (Dennis Looks Like a Registered Sex Offender)

Season Four
After Charlie and Dee steal his deer steak Frank tricks them into eating raccoon meat and makes them think it's human meat. (Mac and Dennis: Manhunters)

Frank is devastated when Mac and Charlie fake their deaths, even carrying a mannequin of Charlie around, speaking to it and even at one point "banging" it. (Mac and Charlie Die (Part 2))

Frank and Charlie argue over who pooped the bed. It turns out to be Frank. (Who Pooped the Bed?)

Frank is excited to be in Charlie's musical as a troll guy, but Charlie is aggravated that Frank wishes to perform naked and pronounces "soul" as "hole". After the Waitress rejects Charlie's proposal, Frank can be heard softly saying "it's okay, Charlie, she ain't worth it. And by the way, I think the rape scene went really well." Charlie tells him if he brings it up at the apartment he will slap him. (The Nightman Cometh)

Season Five
Frank announces he has bought a foreclosed house; Charlie asks Frank in a concerned tone if he's moving out and Frank quickly confirms he is not. (The Gang Exploits the Mortgage Crisis)

Frank announces he has sublet the apartment and has bought an RV with Dee. Charlie says he's not sure if he can live in an RV and Frank retorts he won't need to, apologizing as he leaves. Charlie, now living in a cardboard box down by the docks, is Charlie's "guy" and they happily announce that they're crab fishermen. (The Great Recession)

This season revealed them to be very close best friends, referring to themselves as the "Gruesome Twosome." Charlie is upset that Frank agrees with Mac's ideas for a cleaner apartment, but Frank soon goes back to Charlie's side when Mac suggests they sleep in separate beds and throws out Frank's toe knife. (Mac and Dennis Break Up)

Season Six
Charlie convinces Frank to enter into a same-sex marriage so he can get on Frank's insurance. Frank is not willing to until Charlie offers to never pull the plug on Frank, and gets Carmen to confirm they can both be men in the relationship. (Mac Fights Gay Marriage)

Frank is shown being stingy sharing money with Charlie at the strip club, which further upsets Charlie as their status as a couple wasn't able to get them a discounted lap dance. After a fierce argument about groceries, laundry, and dishes, they decide to get a divorce. With the help of Charlie's lawyer, Uncle Jack Kelly, Frank and Charlie are able to speak civilly and get an annulment. (Dennis Gets Divorced)

Charlie and Frank walk around naked in the sewers together. (Dee Gives Birth)

Season Seven
Frank and Charlie, along with the rest of the gang, sleep in the bar to stay safe during a hurricane. Frank and Charlie sleep in a double sleeping bag together. (The Storm of the Century)

Frank tells a boatload of tourists," Charlie, he's my buddy, we sleep together, we hang out together." (Thunder Gun Express)