Despite being the top promotion in mixed martial arts, the UFC hasn't always rostered the best fighters. In many instances, it has looked to free agency to find new talent.

Some signings have worked out well, but other investments have failed to yield solid returns. Here are 15 free agents who didn't pan out in the UFC.

Mirko "Cro Cop" Filipovic

UFC record: 4-6

"Cro Cop" was the first notable free-agent signing out of Pride FC before the UFC purchased the Japanese-based promotion in 2007. This acquisition was so significant that the UFC announced the signing during its UFC 66 pay-per-view event featuring the rematch between Chuck Liddell and Tito Ortiz.

But Filipovic would never live up to his billing as a future UFC heavyweight champion. The Pride Grand Prix winner was the recipient of one of the most brutal finishes in MMA history when Gabriel Gonzaga landed a head-kick knockout against him at UFC 70.

Despite two separate stints with the UFC, Filipovic never picked up a significant win in the promotion. He is considered by many to be the biggest free-agent bust in UFC history.

Wanderlei Silva

UFC record: 5-8

Silva returned to the UFC in 2007 after an accomplished career under the Pride FC banner that saw him establish himself as one of the top 205-pound fighters in the sport. His opponent in his return fight at UFC 79 would be a longtime rival in Chuck Liddell.

Silva lost that fight by unanimous decision before suffering key defeats against Quinton "Rampage" Jackson and Rich Franklin. A drop to middleweight didn't help much, either. He went 3-2 in that division before issues with the Nevada State Athletic Commission forced the Brazilian to leave the UFC.

Heath Herring

UFC record: 2-3

Herring was another Pride FC heavyweight who looked to rejuvenate one of the UFC's weakest divisions in 2007. Unfortunately, the American's stint was short-lived, lasting just over a year.

The American dropped his promotional debut against Jake O'Brien at UFC Fight Night 8 but went on to win two of his next three bouts. "The Texas Crazy Horse" then replaced Mark Coleman on short notice against Brock Lesnar at UFC 87. The former WWE superstar bulldozed Herring for a three-round decision victory in Lesnar's first UFC win. The former Pride FC title challenger never fought in the Octagon again.

Herring, now 42, took an eight-year hiatus after that fight. He returned to compete for RIZIN in 2016.

Denis Kang

UFC record: 1-2

Canadian middleweight Kang entered the UFC with great promise in 2009 when Anderson Silva was dominating the 185-pound division.

Though Kang showed flashes of talent in his fights against Alan Belcher and Michael Bisping, he ultimately lost both matchups by stoppage. He scored his lone promotion win at UFC 97 with an inconsequential unanimous decision victory over Xavier Foupa-Pokam. The Tristar product's disappointing run prompted the UFC to cut him in December 2009, 11 months after his promotional debut.

Norifumi 'Kid' Yamamoto

UFC record: 0-3, NC

Yamamoto was widely considered one of the best featherweight fighters on the planet in the early 2000s. Unfortunately, the Japanese superstar didn't sign with the UFC until 2011. At age 33, he was arguably past his prime.

"Kid" made his UFC debut against future flyweight champion Demetrious Johnson at UFC 126 and lost by unanimous decision. The Krazy Bee fighter never ended up winning a fight under the UFC banner. He died of stomach cancer in September 2018 at the age of 41.

Tatsuya Kawajiri

UFC record: 3-3

Kawajiri signed with the UFC in 2013 after a 9-2 run across a variety of promotions including Dream, Strikeforce, and One Championship.

The former Shooto lightweight champion enjoyed a great start to his UFC career with three wins in his first four fights, but back-to-back losses to Dennis Bermudez and Cub Swanson halted his momentum. He asked for his UFC release in October 2016.

Though "The Crusher" left the promotion of his own accord, it's unlikely the UFC would've kept him around much longer as he struggled to become a featherweight contender.

Rameau Thierry Sokoudjou

UFC record: 1-2

Sokoudjou was responsible for two of the biggest upsets in MMA history, knocking out Antonio Rogerio Nogueira and Ricardo Arona in back-to-back fights during his tenure with Pride FC.

Signed by the UFC in 2007, "The African Assassin" ended up losing his promotional debut to future light heavyweight champion Lyoto Machida at UFC 79. Sokoudjou went 1-1 in his next two fights before the UFC sent him his walking papers.

Gilbert Yvel

UFC record: 0-3

Another Pride FC export who struggled in the Octagon, Yvel had the tough task of facing future UFC heavyweight champion Junior dos Santos in his promotional debut at UFC 108 in January 2010.

The former Rings openweight champion lost that fight by TKO and went on to lose two straight against Ben Rothwell and Jon Madsen. The UFC released the Dutch striker less than a year after signing him.

Takanori Gomi

UFC record: 4-9

Gomi, a former Pride lightweight champion, never seemed to find his footing in the Octagon after signing with the UFC in January 2010. Facing some stiff competition in Kenny Florian, Nate Diaz, and Joe Lauzon, Gomi never became a contender in the 155-pound weight class.

The UFC released Gomi in October 2017 following five straight losses.

Hector Lombard

UFC record: 3-8, NC

Lombard was the first marquee free agent to come over from Bellator when he signed with the UFC in 2012.

The former Bellator middleweight champion struggled from the get-go, suffering an uninspiring split-decision loss against Tim Boetsch at UFC 149. Despite picking up big wins against Nate Marquardt and Jake Shields, Lombard went winless in his next seven fights before departing the UFC in October.

Marcin Held

UFC record: 1-3

Former Bellator title challenger Held seemed like an underrated signing for the UFC when he came aboard in 2016. The Polish fighter struggled in the Octagon, however, losing three straight fights.

Though he did pick up a lone UFC victory over Nasrat Haqparast at UFC Fight Night 118, the promotion decided to release Held from his contract in late 2017.

Will Brooks

UFC record: 1-3

Brooks came over from Bellator in June 2016, vacating the promotion's lightweight belt. He carried an eight-fight win streak into his UFC debut.

After defeating Ross Pearson at "The Ultimate Fighter 23" finale, the American Top Team product struggled. Brooks lost three consecutive fights to Alex Oliveira, Charles Oliveira, and Nik Lentz. Those setbacks forced the UFC to cut him in late 2017.

Gilbert Melendez

UFC record: 1-5

Melendez had an especially tough run in the UFC, facing the likes of former champions Benson Henderson, Anthony Pettis, and Eddie Alvarez.

But it was a positive test for performance-enhancing drugs in July 2015 that really hurt the former Strikeforce champion's career. The suspension that followed kept "El Nino" on the sidelines for more than a year.

The 37-year-old last competed against Arnold Allen, losing their featherweight bout by unanimous decision at UFC 239 last July. The UFC released Melendez in November after he suffered five straight losses.

David Branch

UFC record: 4-6

Branch rejoined the UFC in 2017 following an incredible run with World Series of Fighting that saw him capture both the middleweight and light heavyweight titles.

After a successful UFC return against Krzysztof Jotko at UFC 211, the Renzo Gracie product suffered three stoppage losses in his next four fights. The 38-year-old tested positive for performance-enhancing drugs in September and was subsequently released from the promotion.

Tarec Saffiedine

UFC record: 2-4

Saffiedine was the last Strikeforce welterweight champion and entered the UFC on an impressive 8-1 run. The Belgian fighter struggled after defeating Hyun Gyu Lim in his promotional debut, however, winning one of his next four bouts.

The 33-year-old last competed in June 2017 when he suffered a unanimous decision loss against Rafael dos Anjos at UFC Fight Night 111, but he wasn't officially released from the promotion until this past November.