Travis has a personality lacking in confidence, despite him being a radio host. Before the events of Confidence Man, Travis will constantly mumble and trail off on Diamond City Radio, and may sometimes shout maniacally (e.g. "OH WE'RE GOING TO DIE!")

Travis's confidence can be changed in Confidence Man, where the Sole Survivor can help Vadim Bobrov to help Travis fight his fears. He has romantic feelings towards Scarlett who works at the Dugout Inn.

Upon completing any quest after Confidence Man Travis's accent will change to that of a Transatlantic accent, and of course, will gain a more confident demeanor.
The Sole Survivor can kill Travis, which leads to Sheng Kawolski taking over the microphone, saying the phrase, "Hey, so uhh... that Travis guy is dead? This is Sheng Kawolski. I guess I'll play the music from now on!" immediately after the song that Travis last announced ends. This will make Diamond City security hostile to the player character, even if they stay hidden and then leave the Diamond City Radio location.
After Confidence Man he will sometimes refer to himself as Travis "Lonely" Miles.

Despite his age, Sheng throws his weight around with any adults he encounters, even calling the player character a "jackass" to their face if they refuse to buy the purified water which he peddles.
During the day Sheng is in charge of Diamond City's water purifying system. At night he goes to the schoolhouse and sits at a desk to take night classes
He will replace Travis Miles as the DJ of Diamond City Radio should Travis be killed during the Confidence Man quest.
Other
Upon first approaching Sheng, the Sole Survivor will find him arguing with one of the Diamond City guards about the purity of the water he's in charge of keeping clean.[4] The player character can ask Sheng for work, whereupon Sheng will give the job of clearing the water around him of any debris that could clog the water filters. Among the miscellaneous junk the player character must find is a human skull. When the job is complete, the player character can confront Sheng about this, which Sheng will casually reply that he may have sent someone else to do the same job before the player character and that perhaps that person found a live grenade.[5]

Diamond City Radio is a radio station in the Commonwealth in 2287, broadcast from Diamond City. The radio station plays a total of 37 songs, excluding Magnolia's songs.
The station plays a wide range of music including pre-War and post-War tracks, with some of the post-War tracks written and performed by Magnolia. The station includes songs from Fallout 3's Galaxy News Radio. It is also the first radio station in the Fallout series to play mainstream 1950's rockabilly music, not just proto and western rockabilly songs which the previous games radio stations were known for. It features the DJ Travis who makes situation-appropriate remarks. If Travis is killed he is replaced by Sheng Kawolski as radio host.

Tracks:
A Wonderful Guy by Tex Beneke, featuring Claire Chatwin (1949)
Accentuate the Positive by Bing Crosby (1945)
Anything Goes by Cole Porter (1934)
Atom Bomb Baby by The Five Stars (1957)
Butcher Pete (Part 1) by Roy Brown (1950)
Butcher Pete (Part 2) by Roy Brown (1950)
Civilization, also called "Bongo Bongo Bongo," by Vic Schoen and his Orchestra Danny Kaye and The Andrews Sisters (1947)
Crawl Out Through the Fallout by Sheldon Allman (1960)
Crazy He Calls Me by Billie Holiday (1949)
Dear Hearts and Gentle People by Bob Crosby & The Bob Cats (1949)
Easy Living by Billie Holiday with Teddy Wilson and his orchestra (1937)
Good Rocking Tonight by Roy Brown with Bob Ogden and his orchestra (1947)
Grandma Plays the Numbers by Wynonie Harris (1949)
Happy Times by Bob Crosby (1949)
He's a Demon, He's a Devil, He's a Doll by Betty Hutton (1950)
I Don't Want to Set the World on Fire by The Ink Spots (1941)
Into Each Life Some Rain Must Fall by Ella Fitzgerald and The Ink Spots (1944)
It's a Man by Betty Hutton (1951)
It's All Over But the Crying by The Ink Spots (1947)
Keep A Knockin by Louis Jordan (1939)
Maybe by The Ink Spots (1940)
Mighty, Mighty Man by Earl Barnes and his Orchestra, featuring Roy Brown (1948)
One More Tomorrow by Marjorie Hughes, featuring Frankie Carle and his Orchestra (1946)
Orange Colored Sky by Stan Kenton, featuring Nat King Cole (1950)
Personality by The Pied Pipers, featuring Johnny Mercer (1946)
Pistol Packin' Mama by Vic Schoen and his Orchestra, featuring Bing Crosby and The Andrews Sisters (1943)
Right Behind You Baby by Ray Smith (1958)
Rocket 69 by Todd Rhodes and His Toddlers, featuring Connie Allen (1951)
Sixty Minute Man by Billy Ward and his Dominoes (1951)
The End of the World by Skeeter Davis (1962)
The Wanderer by Dion (1961)
Undecided by Chick Webb and his Orchestra, featuring Ella Fitzgerald (1938)
Uranium Fever by Elton Britt (1955)
Uranium Rock by Warren Smith (1958)
Way Back Home by Bob Crosby and The Bob Cats (1950)
Whole Lotta Shakin' Goin' On by Big Maybelle (1955)
Worry Worry Worry by The Three Suns, featuring The Sun Maids and Artie Dunn (1949)

Thanks for taking a look at my guide :)
============================================================================
via https://fallout.fandom.com/wiki/Diamond_City_Radio, https://fallout.fandom.com/wiki/Sheng_Kawolski, https://fallout.fandom.com/wiki/Travis_Miles