Danica Mckellar as Trudy
Perhaps one of the most important characters in HIMYM history: Trudy first appeared in the "Pineapple Incident" as the drunken one-night stand who leads Ted (Josh Radnor) on a wild night of barely-remembered shenanigans. After ducking down the fire escape, (and leaving a pineapple on his nightstand!) we later saw Trudy in season three when she may or may not have had a threesome with Ted. The mystery of the pineapple has yet to be solved.
Joe Manganiello as Brad Morris 2x04
As avid brunch lovers, Brad and Marshall (Jason Segel) bonded together at Colombia law school when the two guys were dumped by their girlfriends. Brad has appeared naked on the side of the road, gone on a date with Robin (Cobie Smulders) and was a groomsman at Marshall and Lily's (Alyson Hannigan) wedding. Oh and he tried to destroy Marshall career. Talk about inconsistent!
Bryan Cranston as Hammond Druthers
Ted's pain-the-ass boss in season two, Hammond was rude, pushy, and despised by everyone in the office. When Hammond's design for a building was rejected because it looked exactly like a penis, Ted's design was then selected and he eventually became Hammond's boss.
Lucy Hale as Katie Scherbatsky
Katie came to visit her older sister Robin in New York City for the first time in season two. And speaking of first times, Katie was hoping to lose her virginity to her douchey boyfriend on the trip. Ted is actually the one who convinced her to hold out and wait form someone special and she ended up having a great trip in NYC. Unfortunately we haven't seen Robin's sister since!
Bob Barker as Himself
When he was a little boy, Barney (Neil Patrick Harris) asked his mother about his absent father and she pointed to the TV screen claiming that the CBS game show host, Bob Barker, was his dad. In season two Barney went on The Price is Right, and won both showcases in hopes of making his dad proud and revealing himself as his son. Barney later confessed that he always knew that Bob was not his father, but he chose to believe it because it made him feel special as a child.
Mandy Moore as Amy
In hopes of getting over his breakup with Robin, Ted dated Amy, an edgy, PDA-loving, rule-breaker who convinced a very wasted Ted to get a tattoo. Ted ended up with a tramp stamp butterfly tattoo on his lower back which led him to meet Stella, at the tattoo removal clinic later in season three.
Enrique Igelsias as Gael
Robin's short-term boyfriend that she met on a vacation in Buenos Aries, Gael always found beauty in the little things in life. However, his overly carefree attitude and lack of goals eventually pissed off "city-girl" Robin and she kicked him out of her apartment and her life early in season three.
Britney Spears as Abby
Abby was the receptionist at Stella Zimmerman's dermatology clinic and over the course of Ted's ten week treatment, she fell in love with him while he fell in love with Stella. She was an extremely sensitive person so Ted turned her down, Abby slept with Barney and was upset when he never called her again. This led to a hilarious payback in which Abby would follow Barney around and sabotage his chances of hooking up with any other girls.
James Van Der Beek as Simon Tremblay
Simon was an overly confident Canadian water-park employee who still lived in his mother's basement and had delusions of grandeur that his band, The Foreskins, will make it big one day. He was Robin's first boyfriend and appeared in her sophomore Robin Sparkle's hit music video, "Sandcastles in the Sand." He has only appeared twice in the series, but we'd gladly watch a spinoff staring him and his on-again off-again girlfriend Louise Marsh.
Alan Thicke as Himself
A frequent guest star in the HIMYM universe, Alan Thicke has appeared in four episodes as a parodied-version of himself. Alan worked with Robin numerous times back in her Robin Sparkles days appearing in her "Sandcastles in the Sand" music video as well as her short-lived TV series "Space Teens." It was later revealed that Robin had a huge, all-consuming crush on Alan when growing up which lead to her dark days as Robin Daggers.
Will Forte as Randy Wharmpess
Randy idolized Barney in season three, claiming that he would do anything to be like him, and even avidly read Barney blog, something that no one ever does. Barney briefly replaced Ted with Randy as his wingman but quickly realized that Randy is the absolute worst at flirting with girls. Randy later went on to become a very successful brewer with his beer "Wharmpess."
Laure Prepon as Karen
Ted's on-again-off-again throughout high school and college, Karen was very rude and pretentious woman who brought out the worst in Ted. Both Lily and Marshall passionate hated Karen because she cheated on Ted multiple times, and when the couple briefly got back together in season four, Lily purposefully sabotaged their relationship.
Rachel Bilson as Cindy
Our first real connection to The Mother, Ted began dating a student named Cindy and on the 100th episode we learned that she was actually The Mother's college roommate. Despite being friends, Cindy resented The Mother for always stealing her boyfriends. It became clear that the only qualities of Cindy that Ted liked are those that The Mother imparted onto her. Cindy eventually told Ted to book The Mother's band for Robin and Barney's wedding.
Carrie Underwood as Tiffany
For the longest time Ted was on "the hook" for Tiffany who strung him a long and flirted with him without ever breaking up with her boyfriend. She was sweet and beautiful, but incredibly manipulative and Ted eventually gave up on trying to fully win her affections.
Jennifer Lopez as Anita Appleby 5x17
First appearing on Robin's morning show as the author of the best-selling book Of Course You're Still Single, Take a Look at Yourself You Dumb Slut, Anita was a confident woman who aimed to crush Barney for being a player. Barney tried to break Anita's waiting to have sex rule by planning a "Super Date," but he had a change of heart and gave the date to Robin and Don.
Nicole Scherzinger as Jessica Glitter
Jessica Glitter was Robin's best friend and co-star on the educational (and slightly inappropriate) Canadian show, Space Teens. They sang a duet about their beavers and it was probably the second most amazing song in HIMYM history. ("Let's Go to the Mall" will forever be number one!)
Jorge Garcia as Steve "The Blitz" Henry
"The Blitz" was Ted and Marshall's friend from college who always missed out on the most mind-blowing life experiences. We briefly met him in season six, but we'd love to see him return for Barney and Robin's wedding!
Katy Perry as Honey
Okay so we never really learned her name, but "Honey" was the best way to describe this sweetly naïve girl. She once let her landlord put a security camera in her shower because she thought it meant her building was extra secure. Oh, Honey…
John Lithgow as Jerome Whittaker
After a lifetime of wondering, Barney finally found out that his "Uncle Jerry" was actually his father. True Jerome may not be as legendary as his son (very few people are!) but he is a good man with a kind heart. We have a strong feelings we'll definitely be seeing him at the wedding.
Martin Short as Garrison Cootes
As Marshall's environmental-loving boss, Garrison was great at caring about the planet, but not-so-great at actually being a lawyer. He is currently hiding out in his bunker in Colorado.
Katie Holmes as Naomi aka the Slutty Pumpkin
After seasons and seasons of waiting, we finally met the Tootsie-Roll-loving, Slutty Pumpkin! Although she was perfect on paper, Naomi was not quite a perfect fit for Ted.