Can you tell I like this picture by Justiniano?

Beast Boy 1, p. 5

Gar Logan has been around since November, 1965.  Here are some links to Gar's "official profiles" and some of the best histories on the net.

Data:

What's known on Gar:

Name: Garfield "Gar" Mark Logan

Marital Status: Single (thank God! ^_~ ) 

First Appearance: Doom Patrol #99, November 1965

Known relatives:

Marie Logan (mother - desceased)
Mark Logan (father - desceased)
Unnamed paternal uncle and aunt (status unknown - but must exist, otherwise there would be no cousin)
Matt Logan (cousin)
Rita Farr Dayton (adoptive mother - NOTE that Rita was dead... however, thanks to various factors, she got better)
Steve Dayton (adoptive father)

Hair Color: Green
Eyes: Green

Interesting fact: In Doom Patrol #100, where they show Gar's first origin story, Gar is shown as a child with brown hair. In a later origin story (Doom Patrol #112), he's shown with blonde hair.

Click on the cover image from Who's Who in DC to get Gar's bio sheet from the same issue.

Changeling on the cover of Who's Who in DC

Click for Gar's profile sheet

Titans Secret Files and Origins later provided a slightly updated biography.

Gar by Justiniano, Titans Secret Files and Origins 2 page 37

Click for Gar's profile sheet

Teen Titans/Outsiders Secret Files and Origins 2003 provided the latest biography of Gar, according to Geoff Johns.

Gar by Mike McKone, Teen Titans/Outsiders Secret Files and Origins 2003 cover

Click for Gar's profile sheet - profile sheet image by Carlo Barberi

The best Gar bio on the net at Titanstower.com

Titanstower.com has the best, most comprehensive details on any Titans related character on the net. For me to even try to duplicate it would be futile.  Also remember to check out the Doom Patrol link.

Gar's first ever appearance in Doom Patrol

Beast Boy bio at Answers.com

Beast Boy bio at the  DC Database Project