INFINITE CHALLENGE

There are usually six hosts for this show, but sometimes special guests are invited on certain episodes.
Below are the main characters who host the show.  Below each pictures of the members, you can play their signature songs which were featured in season 3 episode 61-62.

As host-in-chief, he led all Muhan Dojeon members in reaching the goal of each episode. In 2008 he was replaced by Myung-Su Park, but was reinstated as host-in-chief. 

Nickname
Chief Yu (유반장)
The First-in-command (1인자)
The grasshopper (메뚜기)

He is also known as "국민MC" (The BEST TV Host In Korea), because of his role on various TV shows in Korea.

He has continuously procalimed his nickname (Geo-seong 거성, or Giant Star). He is often referred to as "Father" by the rest of the members due to his elderly look and age.  He is also known as "Devil" because of his reactions toward other members.  His character always has been rude and grumpy, but that's just his way of surviving in the entertainment business. 

Nickname
Giant Star Park(거성)
Father (아버지)
The Second-in-command (2인자)
The Son of the Devil (악마의 아들)
Cool Guy (쿨거성)
Sancho Park (산초박)
Alien (외계인)
The leafhopper (벼멸구)
Worthless brother (하찮은 형)
Chief Park (박반장) which did not last long, after Yoo was reinstated he was no longer in chief.

Due to the extraordinary size of his head, he is called "Helmet Jung".  Actually he has the biggest head in the show, sometimes his head is compared to Noh's head who has the second biggest head in the show, but still Jung's head can't not be matched.  He is also known as "The God of Eating" because he eats a big bowl of noodle in under 10 seconds.  On 50th special episode, he finished 50 bowls of hot noodle in 5 minutes.

Nickname
The Helmet (헬멧),
The Lord of Eating (식신)
The Third-in-command (3인자)
Lacking brother (모자란 형)
Stupid brother (바보형)
Mr. Jeong Joong-ang (정중앙씨)

Over many episodes, he has demonstrated his talent in everything imaginable, he is very athletic and intelligent even though he doesn't look that way.   He is also known as "The Unfunny One" in the show, but it was sometimes proven wrong.  He is the original member from the first episode.

Nickname
Awkward Pig (어색한 뚱보)
Arrogant Pig (건방진 뚱보)
Sir. Moon (달님)

Due to his extremely fast speed of speech he was known as "Quick Mouth" but over the time, he developed his crazy side in the show.  He is now more familiar with nick name "Stone Head(돌+i)".  He is the loudest character in the show, and he is becoming more like his mentor "Myung-soo Park" over the years.
Sometimes he is called "Young Devil" due to his harsh comments and criticisms.  He is the original member since the beginning of the show.

Nickname
Quick Mouth (퀵마우스)
Stone Head(돌+i)
Psychopath(싸이코)
Young Devil (젊은 악마)

He is a good friend of Noh.  Noh and Haha were known as "Best Buddies (죽마고우)" for a while.
In 2007, Haha began his military service, which will end sometime in 2009,  he was replaced by Jun-jin.
Many jokes are made about his short height, and his nicknames are mostly based on his height.  He played very important role making the show one of the best comedy shows in Korea before he began his military service.

Nickname
Shorty(단신)
Good Looking One(무한꽃미남)
The Little Kid(꼬마)
Top Little Kid(상꼬맹이) which was named by his own mother.
The Master Degree Ha ha(석사)

Since June 2008, he has replaced Ha Ha. 
As a member of a legendary idol band "Shinhwa" for more than 10 years, it was a real surprise to see him in the show as a regular member.  Due to his good looks and athletic ability, many viewers thought that he was not suitable for the show, but he has proven them wrong. 

Nickname
Junstin (전스틴)
The roll-in kid (굴러들어온 놈)
Jan Jin (잔진)
The Million Dollar Baby (백만돌이)

Executive Producer of Muhan Dojeon
As the pioneer of Korean entertainment, he currently serves a job for 'reactions' which brings some extra fun in the show, by his own captioning work (just before screening each episode).

He usually appears in the show as a cameo,  his  fans capture his appearance and post his pictures on the forums.  It's kinda like "Where is Wally?".
He is the inventor of "Real-Variety" show, and he is the main brain of the show.  His concept of "Real Variety Show" is often copied by other shows, but they just can't compete with his unique ideas.

He is often called "The Real Devil" in the show, because he puts the members to extreme situations and challenges. 

His captions play really important role in the show, he puts his thoughts and his view on his members.  It is another method for him to talk to the viewers and also to the members.

Nickname
TEO

In despite of royal fans opposition, he officially became the 8th member of Mudo.  Many fans were really furious when he started to appear in the show.  They just could not accept him as a member of Mudo.  As a Hip-Hop Artist, he is well known as a singer from hip hop duo "Leessang". 

TEO officially anounced that he is the 8th member of the show.  Due to extended time of the show, he felt that new character is needed to improve the quality of the show, he feels that a new character like Gill will interact with other members to produce different results and situations which are essential to the show.

Gill will play a similar role that Haha played when he was in the show.  TEO stated that he is not the replacement of Junjin who is having a hard time in the show.  He recently told the press that there will be no changes on the casts, Gill will only be an additional member.