CLIFF BURTON

A weird flame snuffed out far too soon, Cliff Burton has been an inspiration to many, many people, not just bass players. His personality, eccentricities (such as embracing flares in the 80s thrash metal scene!), wide musical taste, and general confident charisma were joined with a huge aptitude for the electric bass, both as a player and composer, strengthened by classical music training which brought an imaginative and intelligent undercurrent to his work with Metallica.
The first band of Cliff's that has any known aural evidence remaining was Agents of Misfortune, a kind of psychedelic metal jamband in which he was joined by Jim Martin on guitar (later, of course, to play in Faith No More); before that, Jim and Cliff had a band called EZ Street with Mike Bordin (also later of Faith No More) on drums. I don't know of any EZ Street recordings, but Agents of Misfortune can be witnessed playing and being interviewed for a Battle of the Bands circa 1981 - https://www.youtube.com/watch?v=N1q0zLaXUuE
It's a mixed bag musically, but despite the sloppiness I love it for the sheer balls of making such a slab of semi-improvised nuttery for such an event. It's raw and takes risks and doesn't care what you think, and that's alright by me. Incidentally, you can hear the beginnings of 'For Whom The Bells Toll' and 'Anaesthesia' in there.
Next Cliff joined the band Trauma, but left to join Metallica before their album 'Scratch and Scream' came out. If you look around, you should be able to find demo recordings he made with the band, some of which are included in marginally better sound quality on the recent (and really over-priced) CD reissue of the album; there is also video footage of him with Trauma on youtube. Trauma tend to get short thrift, but in my opinion the album is pretty good in places. They played a generalised form of heavy metal that flirted with proto-thrash and power metal styles. Needless to say though, Cliff certainly made the right move in joining Metallica, who were destined to have a much longer shelf-life, and benefitted hugely from his presence. Cliff's compositional skills lent their newer material a depth of melody and dynamics that helped Metallica stand out from the crowd and begin to truly forge their own path beyond being a Diamond Head cover band (I say that with tongue in cheek, but Metallica fans will know what I mean with no disrespect!).
The most obvious contribution Cliff brought to Metallica was his bass solo, which appeared on their first record 'Kill 'Em All' as 'Anaesthesia (Pulling Teeth)', joined by drums around halfway through and segueing into 'Whiplash'. It's a real tour de force of bass playing with fuzz and wah pedals in full effect, moving from classically informed structural melodics into wild soloing that I'm still trying to equal. This was a high point of live shows, where it would be performed slightly differently each time, as evidenced by the posthumous video/DVD tribute 'Cliff 'Em All'. 'Ride the Lightning' was blessed with his H.P. Lovecraft-inspired 'The Call of Ktulu', and 'Master of Puppets' contained his brilliant composition 'Orion', which never sounded as good played with any other bassist. Tragically, after three albums with Metallica Cliff was killed instantly in a tour-bus accident in Sweden on September 27th, 1986. He remains sadly missed.

Suggested listening:
TRAUMA
Demo I (1982)
METALLICA
Kill 'Em All (1983)
Ride The Lightning (1984)
Master Of Puppets (1986)

JOHN ENTWISTLE

Next up in this British trilogy is the esteemed John Entwistle, who of course was the bassist for The Who until his sudden demise in 2002, the details of which are well known.
The man was known as 'thunderfingers' for a reason! I'm not sure when that nickname first came about, but it was in evidence as early as his thrilling bass solo fills in 'My Generation' in 1965. His bass was also well to the fore in his own composition 'Boris the Spider', a live favourite, and the awesome 'The Ox' (another nick-name!). Although another 'quiet one', just standing there playing with a semi-bored look on his face as he played, the occasional devilish grin would break out for a moment, hinting at the playful energy that welled within. By the end of the 60s his bass sound had grown comfortably with the increase in amplified power and he was a fully assured master of the instrument in a rock context. My favourite moments of his playing are on 'Live At Leeds' from 1970, where you can hear muscular playing that is confidently fluid and exploratory at the same time, with jamming aplenty. Through this his playing remains grounded in the groove of the song and the interplay between musicians is telepathic in that rare way that musos love.
Of his solo albums, I've admittedly only heard the first two, 'Smash Your Head Against The Wall' and 'Whistle Rymes', which are OK but the material failed to make much of an impression on my ears. I was intrigued that he did an album with Glen Tipton of Judas Priest and Cozy Powell (whom despite all his other accomplishments, I always remember just for Bedlam) - 'Edge of the World' - which came out well after both John and Cozy had passed on. However, it's a bit of a mixed bag - great to hear John in a metal context, but not so great with the songs themselves and the mainstream approaches much of the time.
All that being said, the strength of his playing with The Who, especially live, makes up for any mis-steps on the side. John Entwistle will always have a special place in my heart, along with my other favourite players, for being a great player and a great guy.

Suggested listening:
THE WHO
My Generation (1965)
A Quick One (1966)
The Who Sell Out (1967)
Live at Leeds (1970)
Live at the Isle of Wight Festival 1970 (1996)
Who's Next (1971)
SOLO
Smash Your Head Against The Wall (1971)