The character ALF was originally created by Paul Fusco in 1984. He already offered his concept of a sitcom about an alien to the Disney Studios and to the Muppet-creator Jim Henson, but they rejected it, when finally he had a meeting with NBC's Brandon Tartikoff. The NBC executive Warren Littlefield, who was also present at the meeting, later described it as "the funniest presentation he ever saw." The network was convinced to produce the show, and together with co-creator Tom Patchett and executive producer Bernie Brillstein they shot more then 100 episodes.
It is a common misconception that ALF was played by the only 90 cm (around 3 feet) tall Michu Mezaros. But he just portrayed ALF in the first season and part of the second season only when he needed to be seen walking. In normal scenes and in the third and fourth season the producers of the shows used other methods that did not require a costume.
Creator Paul Fusco was always was ALF's voice in the original english version of the show. In the non-english versions of course other people had to be ALF's voice, f.e. Thommy Piper is ALF's german voice, he even recorded several music records as "ALF" including the Top 20 hit "Frohfest". Also ALF viewers from France or spanish-speaking countries report that ALF in their language has its own charme, so it seems like ALF always got an excellent dubbing and is just a great show to enjoy in every language.
Background Info
ALF was originally aired on NBC from 1986 until 1990. It was on always Mondays at 8 p.m., the last part of the fourth season was shown Fridays at 8 p.m. Although the network tv stations normally don't re-run their shows, the first season had been shown again by NBC in their saturday-morning-cartoon-line-up, before the ALF cartoon series came up.

Since 1990, when the last regular ALF episode #102 "Consider Me Gone" was shown, ALF has not been shown that often in the USA. The show has been re-run in the USA in the syndication which means that local TV stations (a different one in every town) showed it again. But of course each one at a different time (only if the local station did it at all). One of the cartoon series had been re-run later on the Family Channel, a cable network.

Since April 3, 1999, ALF was shown again in the USA on a cable network called "Odyssey Channel". Until August 4, 2001, the complete series was shown several times, as was the made-for-TV ALF movie "Project: ALF". I don't know if there are any Nielsen numbers published for this, but it is said that ALF is the #1 rating show on Odyssey Channel. Unfortunately, on August 6 of the year 2001 the Odyssey Channel was renamed into Hallmark Channel and ALF is not longer aired in the United States since then.