Dodge City Marshal Ed Masterson was killed in the line of duty on April 9, 1878.
Masterson was the first Dodge City law enforcement officer to be killed in the line of duty.

 
Maynard Reece Byrd
Dodge City

Ed was Bat's brother MR?
 
I was thinking there was a younger brother killed before Ed.  Or was he just deputized?

Here is the rest of the story(according to Wipiedia)--
Ed Masterson (September 22nd, 1852-April 9th, 1878) was a lawman and the brother of old west personality and gunfighter Bat Masterson, as well as James Masterson.
 
Lawman career
 
Ed Masterson was born in Henryville, Quebec. His family moved to Wichita, Kansas in 1866. Ed Masterson, as reported by those who knew him, never possessed the characteristic personality of his more famous brother, Bat, or his other brother James. He was generally thoughtful and well liked, but not assertive during his service as a lawman, which historians often state as a factor in his death. [1]
Prior to beginning his lawman career, he and his two brothers worked as Buffalo hunters in the northwest. During his service as the marshal and Deputy Marshal of Dodge City, Kansas, Ed Masterson was shot twice, and during both instances he shot his assailant. The first incident occurred in mid-1877, when he was shot in the chest by Bob Shaw in the Lone Star Dance Hall. Shaw was also shot during that incident by Ed, dying later. After Masterson's recovery, he replaced Town Marshal Larry Deger as Marshal. It is commonly believed that he replaced lawman Wyatt Earp, but it was actually Deger. On March 15th, 1878, Masterson assisted his brother Bat, who was the Ford County Sheriff at that time, and lawman Charlie Bassett in the capture of two train robbery suspects. [2]
Later that same month, Masterson announced publicly that he had a new plan to rid Dodge City of vagrancy and street violence, which included the disarming of gun-carrying men inside the city limits, and that it would be implemented immediately. On April 9th, 1878, while attempting to disarm a drunken cowboy, Masterson was shot once in the chest. He returned fire, shooting the cowboy, Jack Wagner, in the hip. Bat Masterson responded, running across the street shooting at both Wagner, and his employer Alf Walker. Ed Masterson died shortly thereafter, after walking into the street and collapsing. Wagner died the next day. Witnesses who saw the killing of Ed Masterson report that it appeared he was carrying a rather pungent cigar in his hand. In actual fact it was the close range muzzle blast from Wagner's gun which had set Ed Masterson's clothes smoldering. There has been some debate as to whether Bat Masterson or Ed shot Walker, meaning was he shot and killed, shot and wounded, or simply shot at and missed. [3] [4]
Masterson was replaced by Charlie Bassett as marshal, with Wyatt Earp, James Earp, and Ed's brother Jim Masterson working as deputies. His brother Jim would later replace Bassett as marshal. Despite common belief, Wyatt Earp never served as the marshal of Dodge City.

Very interesting MR.
 
I believe I'm thinkin of one of Wyatt's brothers.
 
 
Several years back,  who was the old man they found who was thought to be one of the Earps or one of the Mastersons'.   He had been in hiding since he was a young man.  Can't remember what year they found him or where, but he was very much alive.
 
Do you recall the story?